Jackson, 27, managed a paltry 1.5 yards per rush attempt on 28 preseason carries. Injuries have limited him to just two games in two seasons since signing a $4.5 million contract with the Browns after the 2011 lockout.
After sitting out last season with a knee injury, Rainey finished the preseason with 23 carries for 89 yards and two touchdowns.
Undrafted out Arkansas, Johnson rushed for 129 yards and one touchdown on 33 preseason carries.
Both backs are on the smaller side, capable of helping out in the passing game and returning kicks. We suspect Rainey and fullback Chris Ogbonnaya would be next in line if Trent Richardson misses time with injury, which would put the Browns offense in a serious bind. Of course, that would have been the case with Jackson on the roster as well.