SAN FRANCISCO (AP) - The San Francisco 49ers waived running back Thomas Clayton on Sunday, two days after he sustained a serious knee injury in the fourth quarter of Friday night's 17-16 preseason win over the Denver Broncos.
Clayton tore the anterior cruciate ligament in his right knee and will be out for the season. 49ers spokesman Bob Lange said Clayton would have surgery.
The Niners needed the roster spot and signed rookie fullback Bill Rentmeester to replace Clayton. Rentmeester was released by the Chargers on Aug. 5 after signing with San Diego as an undrafted free agent on May 1. If another team doesn't claim Clayton, he stays with the 49ers and would be placed on injured reserve.
"It's always unfortunate when you lose anyone that's trying to make a football team," coach Mike Singletary told reporters after a walkthrough Sunday. "He's just a guy that really works hard. He gives you everything that he has on every down and we know that he had high hopes of being part of the team. When someone like that goes down, it's always a difficult thing to see. So, we'll just have to rehabilitate the knee and go from there."
Clayton was tripped up by Denver cornerback Jack Williams and awkwardly twisted his knee. He was down for several minutes before being carted off the field. Clayton raised his left finger to the fans, grimacing in pain.
Clayton, who was in the running to make the roster as a backup to Frank Gore, was the 49ers' sixth-round draft pick in 2007 and spent most of his first two seasons on the practice squad before being active for the final two games in 2008.
Singletary said the Niners will let Clayton get healthy before deciding whether to bring him back. Clayton should generate plenty of interest elsewhere, too.
"It's hard to miss him," Singletary said. "When you look at him, he's the kind of guy that everything that he's doing you know that he's going as fast as he can go, he's going as hard as he can go and he's just one of those guys that when you look on him on film, you know that you're going to get everything that he has on every play. Every team is looking for somebody that will do that."
Also, Singletary said fullback Zak Keasey would likely miss 8 to 10 weeks after breaking his arm Friday.
Linebacker Patrick Willis participated in the walkthrough, his first work since injuring his ankle on the first day of training camp. His first full practice back will be Monday. Tight end Delanie Walker, nursing a concussion, also is set to return Monday.