Betts joined the club during training camp, was cut before the regular season and then brought back after Reggie Bush broke a bone in his lower right leg in Week 2.
Betts played in eight games, gaining 150 yards on 45 carries with two touchdowns. He also had 23 catches for 141 yards. Betts sat out the past two games with a neck injury and now Bush is back and running back Pierre Thomas appears ready to return.
Mitchell has played seven NFL season with Kansas City, the New York Giants and Buffalo. He has 487 career tackles with 12 sacks and six interceptions.