Cushing appeared to injure his right knee when he slipped chasing Atlanta's Tony Gonzalez after a catch.
He entered the game leading the team with 76 tackles, including seven for losses. He also has three sacks.
Cushing was helped off the field before being looked at on the sideline by trainers and walking to the locker room before halftime.
Receiver Andre Johnson also left the game with a left hamstring injury.
Information from The Associated Press contributed to this report.