Tre Mason has slimmed down to between 195 and 200 pounds.
ESPN Rams reporter Nick Wagoner confirms Tre Mason "looks to be entrenched" as the starting running back.
Rams coach Jeff Fisher says Tre Mason sat on the bench for the first four games of 2014 because he needed to "learn how to play without the football."
Tre Mason rushed for 28 yards on 11 carries in the Rams' Week 17 loss to the Seahawks, adding three catches for 29 yards.
Tre Mason rushed 13 times for 76 yards with a touchdown in Sunday's Week 16 loss to the Giants.
Tre Mason rushed 13 times for 33 yards in the Rams' Week 15 loss to the Cardinals, also losing a fumble.
Tre Mason rushed 20 times for 66 yards in the Rams' Week 14 win over the Redskins.
Tre Mason rushed 14 times for 117 yards and two touchdowns, and caught 3-of-4 targets for 47 yards and an additional TD in the Rams' Week 13 blowout win over the Raiders.
Tre Mason rushed for 62 yards on 16 carries in the Rams' Week 12 loss to the Chargers.
Tre Mason rushed for 113 yards on 29 carries in the Rams' Week 11 win over the Broncos.
Tre Mason rushed for 48 yards on 14 carries in the Rams' Week 10 loss to the Cardinals.
Coach Jeff Fisher said the Rams will continue to use a committee approach at running back.
Tre Mason rushed 19 times for 65 yards in the Rams' shocking Week 9 win over the 49ers.
Tre Mason rushed for 32 yards on seven carries in the Rams' 34-7, Week 8 blowout loss to the Chiefs, adding a one-yard catch.