By Keith Idec

Last-second substitutes typically don’t present greater challenges than original opponents in boxing.

That’s exactly what Mike Borao believes has happened now that the fighter he manages, Matt Korobov, has replaced Willie Monroe Jr. as Jermall Charlo’s opponent. Korobov signed a contract Monday to challenge Charlo for his WBC interim middleweight title Saturday night at Barclays Center in Brooklyn.

“It’s rare that the opponent falls out in a fight of this magnitude,” Borao told BoxingScene.com, “and you end up with a better fight on one week’s notice as a result. But that’s what happened here.”

Monroe, of Rochester, New York, tested positive for a non-exempt testosterone booster during a performance-enhancing drug exam administered recently by the Voluntary Anti-Doping Association. The WBC announced Monday morning that it wouldn’t sanction a championship bout between Monroe (23-3, 6 KOs) and Charlo (27-0, 21 KOs).

The 35-year-old Korobov (28-1, 14 KOs) was set to battle Colombia’s Juan DeAngel (21-9-1, 19 KOs) in a non-televised eight-rounder on the Charlo-Monroe undercard. Because Korobov has had difficulty securing a meaningful fight either at middleweight or super middleweight, Borao arranged for him to appear on the Charlo-Monroe undercard because he knew it would at least afford Korobov the chance to step in for Monroe if necessary.

“When you represent a guy that other boxers avoid like the plague, you have to get creative,” Borao said. “Monroe is a southpaw, so we specifically asked to be on this undercard. I think Korobov has the desire, will and skill to shock the boxing world Saturday night.”

Korobov-DeAngel was to be contested at 162 pounds, just two over the middleweight maximum. Several outlets have erroneously reported that the maximum weight for Korobov-DeAngel was 168 pounds, but Korobov only needs to lose two additional pounds for his shot at Charlo’s title.

“He was contracted to fight on the undercard at 162 pounds,” Borao said. “Despite inaccurate reporting, Korobov does not have to drop an extra eight pounds this week.”

The Charlo-Korobov bout will headline a Premier Boxing Champions tripleheader on FOX (8 p.m. ET/5 p.m. PT). That three-bout broadcast also will include fights featuring Jermall’s twin brother, Jermell Charlo, and heavyweight contender Dominic Breazeale.

Houston’s Jermell Charlo (31-0, 15 KOs) will defend his WBC super welterweight title against Detroit’s Tony Harrison (27-2, 21 KOs) in the 12-round, co-featured fight. Breazeale (19-1, 17 KOs), of Eastvale, California, will meet Miami’s Carlos Negron (20-1, 16 KOs) in the 10-round opener of the show.

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