With the Cardinals leading 6-3 midway through the third quarter, Stanton was sacked by Rams defensive tackle Aaron Donald and his right leg appeared to lock during the tackle. Stanton left the field without putting any weight on the leg and was carted off after a brief examination on the sideline.
If Stanton is unable to return next week, the Cardinals will be forced to use their third different starting quarterback this season. Stanton first replaced Palmer for three games earlier this year when the latter had a nerve injury and became the full-time starter when Palmer tore his ACL in Arizona's Nov. 9 game against the Rams.
Stanton had completed 54.5 percent of his passes this season for 1,602 yards, seven touchdowns and five interceptions before Thursday's game.
Lindley, 25, hasn't appeared in a regular season game since his rookie year of 2012. He was originally drafted by the Cardinals but was cut by the team in August, returning after a stint on the San Diego Chargers' practice squad upon Palmer's season-ending injury.
Thomas, a fourth-round pick of the Cardinals in this year's NFL draft, completed just one of his eight pass attempts against the Broncos in Week 5 but the play went for an 81-yard touchdown.
Arizona entered Thursday at 10-3 and in first place in the NFC West.
- Ben Estes