“You can’t train a chin,” Angelo Dundee once opined.

Despite the renowned trainer’s words, Amir Khan has enlisted the expertise of Freddie Roach to help rebuild his tarnished reputation and improve the punch resistance that saw the 21-year-old lightweight disintegrate in 54 seconds against Breidis Prescott last September.

Roach, who was a resilient fighter educated by Eddie Futch, believes he can toughen up the Brit’s apparently fragile chops.

The Hollywood based trainer has been using techniques derived from martial arts to “try and deaden, or toughen, those nerves on the tip of [Khan’s] jaw.” The method involves applying pressure to Khan’s mandible using an assortment of exercises.

But the main focus at the Wild Card Gym has been trying to tighten up the once-beaten fighter’s porous defense, while maintaining the blistering hand speed and attack-minded style ahead of his comeback bout against Oisin Fagan at the ExCel arena in London this Saturday on a pay-per-view telecast available on SKY TV in the UK.

“He’s got a lot of tools and is unbelievably fast,” says Roach at his crowded gym on Vine Street, which has seen fighters such as Bernard Hopkins and James Toney pass through its narrow doors. “I think the biggest thing with Amir is he just needs not to look for the knockout. That’s when he gets a little lazy and forgets about defense.”

There was a time when it seemed like Khan didn’t need to learn the finer points of the Sweet Science as his rapid-fire combinations simply overwhelmed opponents.

After avenging his 2004 Olympic final defeat to the exceptional Cuban Mario Kindelan, Khan entered the paid ranks under the guidance of promoter Frank Warren and trainer Oliver Harrison. Khan’s route to superstardom looked secure after signing a contract with network TV broadcaster ITV, while mainstream sponsors rushed toward the Muslim fighter of Pakistani heritage who was viewed as the ideal ambassador for a multi-cultural Britain recovering from the July 2005 terrorist attacks.

If Khan’s performances are not always technically proficient, they are certainly entertaining, as evidenced by his back-and-forth struggle with the light punching Willie Limond in July 2007. After Limond sent the Bolton native reeling to the canvas in the sixth round, Khan rallied back to dominate the subsequent two frames, forcing the Scot’s corner to retire their fighter after he suffered a cracked jaw and nose.

But one year later Harrison was axed as trainer and the esoteric former Cuban national coach Jorge Rubio was surprisingly appointed to the post.  The change did little to improve Khan’s punch avoidance as Prescott caught the static fighter with a left hook on route to ruining Khan’s perfect record in Manchester.

Yet Roach believes his protégé’s style can be easily refined.

“When he gets hit with the big shot [in sparring], I tell him why,” he explains. “The thing about him is that he understands. He's a smart kid. If you understand it, you can make the adjustment much more easily.”

During his six week tenure in Los Angeles, Khan, 18-1 (14), sparred with Manny Pacquiao and undefeated junior welterweight Dean Byrne.  During those reportedly intense sessions Roach reckons he has found a new weapon to add to Khan’s arsenal.

“He’s got a beautiful jab; a better jab than [Oscar] De La Hoya,” claims Roach. “Jabs win world titles.”

“Khan’s jab is amazing. The sparring between us has been great,” adds Byrne, a highly-touted prospect from Ireland with a 9-0 (3) résumé.

On Saturday, Khan will be facing another Irishman, and while Byrne is a skilled boxer, Oisin Fagan is a rugged fighter, willing to absorb punches in a vigorous effort to wear down opponents.

“I’m not as skilled as Khan but he’s over-rated, as was proven when Prescott dumped him on the boards for the full count. If an unknown like him can do it, then why can’t I?” states Fagan, 22-5 (13), who has been training with John Breen in Belfast.

The 35-year-old’s buoyancy has been founded on a chequered career comprised of impromptu events and gritty resolve.

After earning a scholarship to study at the University of Science and Arts in Chickasaha, Oklahoma, the Dubliner enrolled for a degree in physical education and political science with the possibility of pursuing a soccer career.  But a leg injury derailed Fagan’s soccer plans and a lack of jobs in Oklahoma meant he would have to return home before his visa expired.

Yet there was one problem. He had no money for a flight to Ireland.

“To get money I went down to this boxing club in Oklahoma City,” Fagan told the Irish Times. “It was called the Badlands Gym. I'd three amateur fights under my belt from back in Dublin. So I just walked in the door and asked this guy to throw me in with anyone. I told him I didn't care who he put me in the ring with. I just needed the money to get me home so I didn't care who it was I was going to fight.”

Fagan was matched with one Sheldon Mosley at the AMC Flea Market in Oklahoma City.  The Irishman wore down his opponent for a fourth round stoppage win, but any thoughts of a flight home were quashed as Fagan left the ring.

“At the end of the fight a school principal came up to me and we started talking,” recalls Fagan. “I told him I was a PE teacher and he said the PE teacher in his school had just left the previous week. He told me to come around to him the following week for an interview. That was a real God thing, I believe. It was crazy. But it was meant to be.”

On the boxing front one fight led to another and Fagan was pitted as fodder against the much hyped Julio Cesar Chavez Junior at the MGM Grand Arena on the Erik Morales-Jesus Chavez undercard.  Fagan lost a four round points verdict, but surprised onlookers with a strong performance and attracted the attention of some minor promoters.

The bouts came thick and fast for Fagan, and soon after he racked up an 11-fight win streak that was ended by a split decision loss to the undefeated former lightweight titlist Paul Spadafora.  The slick stylist struggled to keep the aggressive Fagan at bay, and many ringsiders thought the former champ was lucky to escape with the win.

But the offer to fight Khan in London presents an unexpected opportunity for Fagan, who has had little luck in finding employment since his return to a weakening Irish jobs market.

“I came back home in the summer and I’ve come back to a terrible economy,” says Fagan, who has been living with his parents in Dublin since his return. “I was finding it hard to get a job at home since coming back so the Khan fight came along at just the right time for me.”

Looking back, Fagan feels he may not be playing the role of opponent if he had a bigger promotional presence earlier in his career, which may have helped swing some of the close points verdicts that have gone against him.

“I’ve never really had a big promoter backing me or a big sponsor. I'm not bitter about that but you wonder what it might be like to have that behind you,” he reflects.

Conversely, Khan has had no shortage of big name backers, and his handlers deem Fagan a suitable opponent to showcase their fighter’s newfound skills.

With all the hype surrounding Khan’s chin, it may be Fagan’s punch resistance that grabs the headlines on Saturday.  The Irishman has a limited offense, but has been stopped only once in his career, and that was in his fourth fight when a butt from Isaac Mendoza broke Fagan’s nose and damaged his cheekbone. Fagan admonished calls for the fight to be stopped, but was bleeding with such perfusion that the referee halted the contest with just forty seconds remaining.

Yet a stout determination doesn’t necessarily win fights, and Roach has been working on a punch that could take advantage of Fagan’s lack of speed.

“I was also working with [Amir] on a left hook,” Roach told The Observer. “[It’s] a little counter shot. When he's facing someone slower than him, when they throw a lazy jab out there, he can let go a hook over the top of the jab, with his elbow higher. He delivers it actually when the [opponent’s] jab starts to come back. It’s a timing shot, a very calculated shot. It was one of the favorite moves of my trainer, Eddie Futch.”

But nobody from the Wild Card Gym will be shouting advice to Khan on Saturday, as Roach will be in Las Vegas for the De La Hoya-Pacquiao showdown and his assistant Gary Stretch is unable to travel to London due to “politics”.

“It’s nothing to do with me and Amir, politics has got in the way,” Stretch, a former British 154-pound titlist who was trained by Roach, told the BBC on Monday. “I was all ready to go, but on the day of the flight [from LA to the UK] I got a phone call and it was Freddie asking me not to go. I have to honor Freddie.”

Frank Warren’s chief matchmaker Dean Powell will now resume his role as Khan’s chief second. Powell prepared Khan for the up-and-down tussle with Michael Gomez last June but his coaching ability isn’t rated too highly by Stretch.

“Dean Powell is a good second, but he doesn’t really know boxing,” said Stretch.

Stretch added that Khan will return to the Wild Card Gym after Saturday’s bout, but the mysterious circumstances surrounding his sudden departure from Khan’s corner has raised doubts about the relationship between the fighter and his new training team.

Frank Warren had earlier attempted to get Khan a fight on the Vegas undercard, but negotiations broke down when Golden Boy Promotions insisted that the Warren-promoted Nicky Cook defend his WBO 122-pound title on the show. Warren balked and instead intended on putting both Khan and Cook on his London card, but that show has deteriorated since injuries saw Cook withdraw from his fight with Stephen Foster and Jonathon Banks pull out of a bout with Enzo Maccarinelli.

Logistically, it has been a complex time for Khan, and Fagan should give him a few more headaches on Saturday.