Baltimore announced the roster moves on Saturday.
Collins, 24, had 411 yards and seven scores on the ground in 10 starts this season. He also had 105 yards and a score on 15 receptions. He sat out the Ravens' Week 12 game due to a foot injury and has not been practicing.
Dixon landed on injured reserve on Sept. 12 with a knee injury. He had 13 carries for 44 yards and a score in the Ravens' season-opening win against the Buffalo Bills. He also missed the 2017 season with a knee injury.
The Ravens battle the Atlanta Falcons at 1 p.m. on Sunday at Mercedes-Benz Stadium in Atlanta.