The quarterback will have will have season-ending surgery for a torn ligament in his left knee, a major blow to a team seeking its first winning record in a decade. He was hurt in the fourth quarter of Sunday's 30-15 loss at Carolina that dropped the Rams to 3-4.
"Even if Sam wasn't hurt, we'd still have some heavy lifting to do," centre Scott Wells said after the game. "But this adds extra to it."
The extent of the injury was revealed on an MRI exam late Sunday after the return flight, and the team announced the results Monday. Coach Jeff Fisher was to provide details at an afternoon news conference.
Bradford tore his anterior cruciate ligament when he landed on his knee after being shoved out of bounds by safety Mike Mitchell. Fisher said after the game that Bradford was in "significant pain" on the sideline. Teammates feared the worst once they saw him carted off the field and on crutches in the locker room.
Kellen Clemens filled in for Bradford and is the only other quarterback on the roster, with the team a week away from a Monday night home game against the Seahawks. Austin Davis, released late in training camp, is perhaps the leading potential backup.
Bradford has 14 touchdown passes and just four interceptions this season. Still, he has his detractors, critics who insist he has not measured up to the billing of a No. 1 overall pick.
But now in his fourth season out of Oklahoma, Bradford has been nudging his way up the ladder, surely among the top half of the league's best quarterbacks. He's been taking charge and minimizing mistakes — exactly what the youngest team in the NFL needed.
Bradford threw for 255 yards and a score Sunday, with one interception and two sacks. He has thrown a touchdown pass in 11 consecutive games. St. Louis had won its previous two games, with Bradford throwing three TD passes in each.
Bradford is no stranger to injuries. He missed six games with a high left ankle sprain in 2011. He had season-ending shoulder surgery in 2009 when he was at Oklahoma.
Clemens made three starts in 2011 but hadn't played this year until replacing Bradford against Carolina. He has made 12 career starts, seven of them with the New York Jets in 2007.
"It's never easy when you see a teammate go down," he said after the game. "When you see a person that you spend as much time with as I do with Sam and genuinely care about as a person. ... I have great respect for what he does on the field, but just as genuine concern for him as a person."
AP NFL website: www.pro32.ap.org