The Rams ended up winning by that final score.
The Browns announced that McCown was out with a right shoulder injury.
McCown left the field on the Browns' previous possession after a sack and fumble, which St. Louis recovered. McCown did not use his right arm at all and was taken into the locker room shortly after.
It was Manziel's first game action since he started in a victory over Tennessee in the second game of the season.
McCown completed 26-of-32 for 270 yards with no touchdown or interceptions. He was sacked four times and lost two fumbles.