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During his time in San Francisco, 49ers running back Raheem Mostert has been an explosive and efficient player. He's averaged at least 5 yards per carry in each of the three seasons where he has been part of the team's running back rotation, and he's had some monster games along the way -- including a 220-yard, four-touchdown outburst against the Green Bay Packers in the NFC title game two years ago. 

But because Mostert got a bit of a later start to his career as a non-special-teamer, he's heading into his age-29 season despite really only being part of the offense for three years. That's right around the age where running backs typically decline, so when Mostert was spotted at Niners camp wearing a brace on his knee, it raised some alarm bells -- especially because he was limited to only eight games last season due to various injuries. 

Mostert, though, saw those alarm bells go off, and was not all that happy about it. It appears that he's been wearing the brace on his knee during practice for a while now, and it has nothing to do with any recent injury that could affect him this season. 

Here's the full quote, via Mostert himself on Twitter

I'm going to address this one time and one time only. I am NOT injured and to the media trying to make something out of NOTHING, I won't allow it. I wear a knee brace in practice for PREVENTION and for my LONGEVITY in this league. I had this brace made YEARS AGO and wore… it in other training camps/practices. Why is it a focus now? I won't allow you to put me into your "hole" of being old, washed up, and injured. I'm just getting started!!

Mostert enters the 2021 season as one of the Niners' lead backs once again. Each of Tevin Coleman and Matt Breida has left the team via free agency or trade, while Jeff Wilson Jr. is dealing with a torn meniscus that could keep him out for part of the regular season. Mostert figures to share the workload with rookie back Trey Sermon, but given his experience and the trust he engenders from Kyle Shanahan, he should be heavily involved throughout the year. It's a good sign for San Francisco that his knee is apparently not anything to worry about.