"He's got a torn patella," Spagnuolo said. "So that's unfortunate for us."
"I got kicked right in the knee," Clayton told *The St. Louis Post-Dispatch*. "And as soon as he did it, (the knee) was like so hot and I couldn't move anything, so it knew it was pretty serious."
Clayton, acquired in a trade with the Baltimore Ravens on Sept. 6, caught 22 passes for 300 yards and two touchdowns in his first four games for the Rams. Clayton, who was targeted 15 times in the Rams' Week 4 victory over the Seattle Seahawks, was the team's leading receiver in each of those categories.
"We certainly don't feel good about losing Mark because he's made a lot of plays for us, but we have to find a way to overcome that somehow," Spagnuolo said.
In Clayton's six seasons, including five with Baltimore, the former first-round draft pick had 257 receptions and 14 touchdowns in 81 career games. He clearly had established a good rapport with Bradford, the No. 1 overall pick and a rising star for the struggling franchise.
"I'd be lying if I said (losing Clayton) wasn't big," Bradford told The Post-Dispatch. "I think everyone has seen what he's done for this offense the first four games of the season. So to lose him, it's definitely going to hurt. But him going down just gives someone an opportunity to step up."
Spagnuolo mentioned practice-squad wide receiver Danario Alexander, an undrafted rookie from Missouri, as a possibility to fill Clayton's roster spot.
Alexander, who had 113 receptions for 1,781 yards and 14 touchdowns during his senior season in 2009 at Missouri, is working his way back after knee surgery in the spring.
"We'll certainly look at Danario," Spagnuolo said. "He's excited about doing it. We want to make sure he's OK physically."
"I'm disappointed in the loss, and I'm really upset the fact that how we lost and by how much and all of that," Spagnuolo said. "These guys feel the same way, so we're in here trying to get it corrected."
Spagnuolo also said starting left guard Jacob Bell and tight end Darcy Johnson, who started two games this season, both have symptoms of concussions. The coach said Bell felt good Monday.
Copyright 2010 by The Associated Press