Mostert submitted a trade request to the 49ers on Wednesday, Adam Schefter of ESPN reports.
Mostert's request comes via his agent, Brett Tessler, following what Tessler describes as "months of unproductive talks with the 49ers about fairly adjusting" the running back's contract. Following the team's trade of Matt Breida to Miami earlier in the offseason, San Francisco's other backfield options currently include Tevin Coleman, Jerick McKinnon and Jeff Wilson.