Following St. Louis' 23-13 win, Rams coach Jeff Fisher said the team's expectation is that Long's injury is serious.
"We anticipate the worst for Jake," Fisher said. "We'll confirm [it but] we're suspecting he has a torn ACL."
Long suffered the knee injury on a 3rd-and-8 pass play in which he was blocking for quarterback Kellen Clemens. There was no obvious reason for the injury, but Long clearly was in pain after falling down.
Long has started all 15 games this season after signing a four-year deal with St. Louis in March.