PHOENIX — Arizona Cardinals quarterback Carson Palmer left the sideline area on a mobilized cart with an apparent knee injury in the fourth quarter of Sunday’s game against the St. Louis Rams.

Palmer moved up in the pocket to avoid blitzing safety Mark Barron, who swiped in Palmer’s direction as the 34-year-old quarterback crumbled to the turf on his backside in obvious pain.

Palmer walked to the sideline but was taken to the locker room on a cart.

The injury comes days after the Cardinals signed Palmer to a $50 million contract extension with $20.5 million guaranteed and an annual salary range of $15.9 million to $16.6 million over the next three seasons.

Palmer would have become a free agent after the 2014 season if he had not agreed to an extension.

He was making a base salary of $9 million, with a $1 million roster bonus, before the extension.

“Carson has played at an incredibly high level and has been a huge part of the team’s success,” Cardinals general manager Steve Keim said. “When you combine his on-field performance with the leadership, stability and professionalism he brings to our team, there was no question that we wanted to extend the relationship and we are excited he felt the same way.”

The Cardinals acquired Palmer from the Oakland Raiders in a trade before the start of the 2013 season. He has led Arizona to a 7-1 record, and the Cardinals are 5-0 in the games yjsy Palmer played.

In Palmer’s last 14 starts dating to the middle of the 2013 season, Arizona is 12-2.

Palmer has completed 64.7 percent of his passes this season, with 11 touchdowns and two interceptions. He has a streak of touchdown passes in 18 games that ties him with New England quarterback Tom Brady for the fourth longest streak in NFL history.

In 142 career NFL starts, Palmer has completed 62.5 percent of his passes for 35,124 yards with 222 touchdowns and 154 interceptions.