ALLENTOWN, Pennsylvania – It’s highly unusual for a 39-year-old boxer to drop down to compete at a new weight.

But that’s exactly what Guillermo Rigondeaux will do Saturday night. The Cuban southpaw, a longtime champion at 122 pounds, will make his bantamweight debut when he opposes Panama’s Liborio Solis in a 12-round fight for the vacant WBA world 118-pound championship at PPL Center.

The 37-year-old Solis has fought at the bantamweight limit or lower many times during a pro career that began in December 2000. Showtime will televise Rigondeaux-Solis as part of a tripleheader that’ll feature WBC featherweight champion Gary Russell Jr. (30-1, 18 KOs) and mandatory challenger Tugstsogt Nyambayar (11-0, 9 KOs) in the main event.

“This, 100 percent, has always been my weight,” Rigondeaux said Thursday during a press conference at the Renaissance Allentown. “It just so happens that at 122, I was doing well. But my weight has always been 118 and I’m gonna dominate this division.”

Dominating a division that includes Japanese star Naoya Inoue (19-0, 16 KOs) and Mexico’s Luis Nery (30-0, 24 KOs) obviously will be an extremely tough task, but Rigondeaux expects to become a unified champion at 118 pounds, too.

“My true weight is 118 pounds and I’m gonna unify [in] this division,” Rigondeaux said. “There’s no question about it and I’m excited to do it.”

Rigondeaux moved all the way up to the super featherweight maximum of 130 pounds to fight fellow two-time Olympic gold medalist Vasiliy Lomachenko in December 2017. That risk resulted in the lone loss of Rigondeaux’s 10-year pro career, a technical knockout after Rigondeaux declined to continue after the sixth round.

His trainer, Ronnie Shields, knows Rigondeaux is a completely different fighter at lower weights, though.

“The guy walks around at 121,” Shields told BoxingScene.com. “That’s what he’s done for the last 10 years, so making 118 is no problem. I put him on the scale before we left [Houston] and he was 117½. I told him, ‘Come on, you’ve gotta eat.’ He said, ‘I am!’ He’s a natural bantamweight.

“Now he’s going down to where he’s most comfortable. He’s strong at 118 and you’re gonna see that his boxing skills are just gonna overmatch everybody in this division.”

Miami’s Rigondeaux (19-1, 13 KOs, 1 NC) is consistently listed as a 6-1 favorite to defeat Solis (30-5-1, 14 KOs, 1 NC) in the second of three fights Showtime will televise, starting at 9 p.m. ET/6 p.m. PT.

Keith Idec is a senior writer/columnist for BoxingScene.com. He can be reached on Twitter @Idecboxing.