Manziel was hit in the head by a defender's knee while trying to make a tackle on an interception return.
Johnny Manziel suffered a head injury and was taken to the locker room during a Memphis Express game against the Orlando Apollos on Saturday.
After Manziel's first touchdown pass was waved off for offensive pass interference, the former Texas A&M quarterback threw an interception in the end zone. During Will Hill III's return, Manziel attempted to make a tackle and instead made contact with Hill's knee.
Manziel had to be helped off the field. He was taken to the locker room and ruled out for the game.
Manziel was 2-of-3 for 13 yards and had three carries for 18 yards before leaving the game.
The former Heisman trophy winner joined the Alliance of American Football on March 16.