Mostert isn't playing in Saturday's preseason game against Las Vegas, Daniel Oyefusi of the Miami Herald reports.
Chase Edmonds got the start and played the first 10 snaps, with Sony Michel then following him into the game. This may just be a matter of caution after Mostert suffered a serious knee injury last year with the 49ers. Most reports suggest the Dolphins will open the season with a backfield committee, though it isn't clear to what extent Mostert specifically will be involved. Edmonds is the sure bet to have a significant role, with his workload likely including a lot of the pass snaps and thus RB targets.