Long suffered the knee injury and was carted off the field in first quarter of the Rams' 23-13 win against the Tampa Bay Buccaneers on Sunday.
Long started all 15 games this season after signing a four-year deal with the Rams in March. He was the first overall selection in the first round by the Miami Dolphins in the 2008 NFL Draft.
"Jake played well for us. He really shored up that side of the offensive line and gave Rodger an opportunity to move over." Fisher said. "I would have confidence in him coming back. He's an exceptional athlete and takes care of himself."BURKE: NFL Playoff Picture through Week 16