PBC’s first show under its new deal with FOX Sports won’t take place as originally planned.

Jermall Charlo was slated to fight Willie Monroe Jr. in the main event Saturday in Brooklyn, New York, on free-to-air FOX, but that fight will likely be scrapped, sources told The Ring. Charlo (27-0, 21 knockouts) holds the WBC’s interim middleweight title, so each fighter was subjected to comprehensive drug testing under the auspices of the Voluntary Anti-Doping Association.

There was an adverse finding in Monroe’s urine sample, the WBC announced Saturday, moments after all parties involved were notified. Monroe hasn’t officially been pulled from the fight by the WBC yet, but that’s expected to happen in the coming days, per sources. The WBC announced that a decision will be made Monday.

Matt Korobov, who is scheduled to fight Juan De Angel in an eight-round super middleweight bout on the off-TV undercard, has already agreed to terms for a fight with Charlo.

Capable fighters who can step in on short notice — in this case Korobov — are usually booked for undercards of major bouts for situations like this. Korobov now will have six days to trim himself to 160 pounds rather than 168-pound limit he was originally ticketed for.

The new fight might be better than original matchup. Monroe is a tricky fighter who has been involved in many aesthetically displeasing bouts. Korobov, on the other hand, is a pressure fighter with impressive amatuer credentials.

The 35-year-old claimed gold at the World Championships twice. The Russian owns a victory over reigning super middleweight titleholder Jose Uzcategui. His lone professional defeat came via knockout to Andy Lee in his first bid to win a middleweight title. Korobov (28-1, 14 KOs) was up on the cards when he was caught by a counter right hook in a fight televised by HBO.

Charlo, The Ring’s No. 6 fighter, is on the cusp of a significant middleweight fight. He held a title at 154 pounds, and he’s been just as destructive with his fists at 160 pounds. He owns quick KO victories over Jorge Heiland and Hugo Centeno. Korobov represents his toughest test yet at 160 pounds, even if it isn’t the high-profile bout Charlo seeks.

“1 week away,” Charlo tweeted. “No matter what I’ll be ready for whoever!”

His twin brother, junior middleweight titleholder Jermell, fights Tony Harrison in the co-feature.