If Lewis has torn triceps, it could be a season-ending injury for the two-time NFL Defensive Player of the Year. It's also unknown how this injury would affect the long-term future of Lewis, 37, who has refused to talk about his retirement plans.
Lewis, who led the Ravens with 14 tackles in Sunday's 31-29 win over the Cowboys, stood on the sideline as the Ravens defense was trying to make a last-minute defensive stand against Dallas. He didn't speak to reporters after the game because he was undergoing treatment.
Entering Sunday's game, Lewis had been criticized for his declining play.
Last season, the Ravens went 4-0 last season when Lewis was sidelined with a foot injury.