But according to head coach Jeff Fisher, via ESPN's Nick Wagoner, Mason will probably be "a game-time decision" for Week 1.
That's certainly good news for the Rams, who expected Mason to shoulder the load until Gurley works his way back from injury.
Mason turned in a solid rookie season with 765 rushing yards (4.3 yards per carry) and four scores, plus another 148 yards receiving and a touchdown. For an offense still working in Nick Foles, and a number of guys along the offensive line, having Mason - a familiar face - in the backfield ready for Week 1 would be a boon to the offense. It could be a tough go against the Seahawks defense in Week 1.