And he doesn't intend to.
Instead, Mostert and the 49ers have agreed upon a new three-year deal that will keep the running back with the team through 2021, according to his agent, Brett Tessler.
The original plan was to gauge market interest in Mostert, which Tessler says was "strong." Other teams had until April 19 to make Mostert an offer, which the 49ers would have the option of matching.
Tessler added that his client "wanted to continue building on what he started" with the 49ers.
Update: Ian Rapoport of NFL Network provides the following information about the new contract.
Mostert initially signed with the 49ers on November 28, 2016, and primarily served as a special teams standout before things changed this past year. Injuries at running back pushed Mostert to gather more playing time on offense. He was having his best NFL season rushing the football before suffering a fractured right forearm during a Week 9 contest against the Oakland Raiders.
"We went into this year just with Raheem mainly as a special teams guy," head coach Kyle Shanahan said in December. "The games that he played in where he got a go at running back, he did a hell of a job."
Mostert finished 2018 with career-highs of 261 rushing yards on 34 carries (7.7 yards per carry) with a touchdown while adding six catches for 25 receiving yards through nine games.
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