Maybe it's too good to be true that former lightweight titleholder Brandon Rios and former featherweight titlist Yuriorkis Gamboa, due to jump up two weight classes from featherweight, would meet in a battle for a vacant lightweight belt on April 14 on HBO.

It's one of the most anticipated fights on the upcoming boxing calendar, but after what happened on Monday, who knows if it will happen?

Top Rank, which promotes the undefeated fighters, sure sounded concerned. So, too, did HBO. And both should be.

Top Rank was blindsided, as were Rios and his trainer (Robert Garcia) and manager (Cameron Dunkin), when Gamboa was a no-show at Monday's news conference to kick off the promotion in Miami, Gamboa's adopted hometown. Rios (29-0-1, 22 KOs) and his team were there, as were members of the Top Rank staff to run the event, but they had no idea Gamboa would blow it off, apparently without explanation, although Gamboa couldn't be reached for comment.

"All I can tell you is, he wasn't here and I don't know why he wasn't here," Top Rank spokesman Lee Samuels told me from Miami. "We have no answers."

Samuels said somebody from Gamboa's team informed them only a few minutes before the news conference was set to begin that Gamboa (21-0, 16 KOs), for reasons they also said they didn't know, wouldn't be coming.

Rios-Gamboa is such a hot fight -- one that matches two of boxing's most exciting fighters -- that Top Rank took the unusual step of putting together a two-city media tour to promote the bout -- Monday in Miami and Tuesday in Los Angeles, the area where Rios is from. Multiple-city media tours are normally reserved for pay-per-view fights.

The bout was announced three weeks ago to much fanfare, and tickets went on sale Friday. Top Rank president Todd duBoef described the initial sales for the fight, due to take place at Mandalay Bay in Las Vegas, as "terrific" and "better than we expected."

But then Gamboa didn't show up for the news conference. It's extremely rare -- frankly, I can't think of a single example in my time on the boxing beat -- for a main event fighter not to show up at a news conference to kick off a promotion when there was no travel issue or illness.

In fact, according to duBoef, one of the things Gamboa asked for when they were closing their deal was that a news conference be held in Miami, which duBoef said he was happy to agree to.

The promotion is supposed to move on to Los Angeles for another media event Tuesday. Top Rank's staff and Rios' team boarded their planes Monday afternoon for the trip, but it's anyone's guess whether Gamboa will show up in L.A.

"All I know is, we are going with Brandon to Los Angeles and we will be ready for another press conference on Tuesday," Samuels said. "Will Gamboa be there? I don't know what to tell you."

The industry scuttlebutt is that Gamboa is pulling out of the fight and perhaps is being wooed by Floyd Mayweather Jr.'s Mayweather Promotions. Whatever Gamboa does, duBoef said he has a firm promotional contract with him.

Knowing how Top Rank usually conducts its business, I have no doubt it has a solid contract with Gamboa. Just look what happened last year when Nonito Donaire tried to leave the company to sign with Golden Boy. They wound up in arbitration and Top Rank's contract was upheld.

DuBoef said Gamboa had agreed to the Rios fight and that he has an ample paperwork trail to back it up, even though the official bout agreement isn't signed yet. (It's standard practice in boxing for a formal bout agreement to go unsigned until well into a promotion.)

DuBoef said he has also been in touch with HBO to inform executives there what little he knows about the situation. Like boxing fans, duBoef hopes Gamboa has a good excuse for his non-appearance and makes it to Los Angeles.

"Where in the world is Waldo? I have no idea. Somebody let me know," duBoef said. "I'll be in L.A. for a press conference on Tuesday. I'll let you know if he shows up."