Byrd-Williamson done.

Heavyweight titlist Chris Byrd signed a bout agreement Friday to face mandatory challenger DaVarryl Williamson. The bout agreement calls for the fight to take place Sept. 30 or Oct. 1 in St. Louis. However, promoter Don King and Showtime are working behind the scenes to add the fight to Showtime’s Oct. 1 card in Reno. That would give the network a tripleheader to go head-to-head with the Antonio Tarver-Roy Jones rubber match being televised on HBO PPV. Showtime also is airing heavyweight James Toney vs. Dominick Guinn and bantamweight champ Rafael Marquez vs. Silence Mabuza. If Byrd-Williamson lands on the Showtime date, it would serve as a prelude to Byrd facing fellow Michigan native Toney in a significant title defense early next year. Byrd signed the bout agreement to face Williamson, his former sparring partner, reluctantly because although his minimum purse under his contract with King calls for $2.5 million, he’s fighting Williamson for $425,425. That’s because his minimum doesn’t come into play if a fight is won at a purse bid. King was the only bidder, winning it for $500,500. Williamson gets the remaining $75,075.