"Not good," coach Chan Gailey said following the game, without divulging the nature of the injury or what ankle Evans had hurt.
Gailey said Evans will miss at least Buffalo's game at Miami next weekend, and wasn't sure when the player might be healthy to return.
Evans was hurt in the second quarter at the end of Jonathan Stupar's 35-yard reception. Evans was attempting to hold off a defender from catching Stupar from behind when he fell awkwardly while appearing to trip over Stupar's leg.
After being tended to on the Bills sideline, Evans returned to the field as if to line up for a play, but then inexplicably ran off and up the tunnel to the locker room.
The seven-year veteran is second on the team with 37 catches for 578 yards and four touchdowns. He has never missed a game in his career, having played in 109 straight games, including 71 consecutive starts.
He finished without a catch on Sunday for only the fifth time of his career, and second time in 12 games.
Browns linebacker David Bowens did not return after sustaining a head injury in the fourth quarter. He was hurt while lowering his head and making the initial hit in preventing running back Fred Jackson from scoring on a third-and-goal from the 1.
Bowens was on the field for several minutes before being helped off to the sideline.
Coach Eric Mangini had no update on Bowens' status.