Saturday night Julio Diaz is facing the kind of fight that is dangerous primarily because it doesn’t seem to be.

Originally the former IBF lightweight champion was supposed to face former champion Joel Casamayor in a crossroads fight for both of them. The winner would have re-established himself as a title contender in the 135-pound division not long after a significant defeat, while the loser would have confirmed to the fistic world that it was time for the division to look for new faces in the crowd.

But the 37-year-old Casamayor was forced to pull out of the Golden Boy Promotions “Lightweight Lightning’’ pay-per-view show with a bad back and that has left Diaz with a far lesser opponent in Rolando Reyes. And therein lies a dangerous dilemma for Diaz.

Reyes (30-4-2, 19 KO) is a decent fighter but not the kind of opponent against whom Diaz can elevate himself with a victory. Although he has won nine of his last 10 fights, Reyes fought only once in each of the past two years and although he won both times they were not against formidable opposition. His victory over Stevie Johnston was not a win over the Johnston who was once a world champion but rather a 35-year-old shadow of who that fighter used to be and thus must be seriously discounted as a measuring stick for what Reyes figures to bring to the ring.

Yet Reyes is dangerous to Diaz on two levels. First, he is good enough to win if Diaz is not fully focused on his job and attentive to it. Second, this is the kind of fight that can put a man in Diaz’s situation out of focus because it is a great disappointment not to be facing Casamayor and instead ending up with an opponent who can do you no good, but can do you great harm if he upsets you.

Diaz has long been considered a talented fighter but one who is a notch below the best lightweights in the world. This seems true even though he twice won the International Boxing Federation portion of the 135-pound championship because in his biggest nights he has consistently come up just a little short.

That was true when he lost a split decision in 2001 to Angel Manfredy in an IBF elimination fight and truer still when he was stopped by Jose Luis Castillo in 2005 when Castillo held the WBC’s version of the lightweight title.

But it was most apparent a year and a half a go when Diaz retired on his stool after eight hard and one-sided rounds against Juan Diaz in a unification fight. Julio had won the vacant IBF title a second time from Ricky Quiles and stopped Jesus Chavez to retain it in his first title defense, so meeting his fellow Diaz in a fight that would give the winner three of the four major lightweight titles (WBA, IBF, WBO) was clearly the most significant moment of the Coachella, Calif. native’s career and he simply was not up to the task.

That night Julio Diaz didn’t look like he belonged in the same ring with his namesake, later insisting, “That wasn’t Julio Diaz in there tonight.’’ Maybe not, but it looked like him. At least it did until the fight started.

Ever since Diaz has been seeking a redemptive moment and  he thought he had it with Casamayor, who although clearly on the shady side of the street still held enough sway with the public and with boxing insiders to make a victory over him enough to rebuild Diaz’s resume and lift him back into title contention.

Now that opportunity is gone and in its place stands an opponent from whom Diaz can gain little but against whom he can lose much. Such moments are a stern test of a man’s fighting character. Many fighters facing similar situations have wavered, slipping on a night like this and seeing their last tenuous hold on a title shot disappear from them not because they weren’t good enough but because they allowed disappointment to beat them mentally before the real fight began.

The mind is a tricky thing in boxing. It can be an enemy as easily as an ally and Diaz needs to understand that in the final hours before he faces Rolando Reyes because, frankly, that is where this fight will be decided. It will be decided in the mind of Julio Diaz.

If he is ready to fight and focused on his job and not what his job might have been, he wins. If he broods over what Reyes is not, he may well lose to what Reyes is.

The lightweight division today is loaded with talent. Juan Manuel Marquez is the man everyone wants to face but there is also Joan Guzman (29-0), Juan Diaz (34-2), Amir Khan (19-1), Michael Katsidis, Casamayor (36-4-1) and the man headlining the “Lightweight Lightning’’ show in Austin, undefeated former junior lightweight champion Edwin Valero (24-0, 24 KO). Clearly there is money to be made here for Diaz but only if he can continue what has been a two-fight resurrection.

It is one thing to lose a fight like the one against Diaz and then claim it wasn’t you in there and quite another to come up short Saturday night. Lose to someone like Rolando Reyes, who is clearly a journeyman at his trade rather than a master craftsman, and there is nothing more to be said and very few places left to go, except to the back of what is becoming a long line of lightweights looking for the same thing Julio Diaz wants – another chance to prove you’re more than people think you are.