Dorsey went down during the 49ers' first defensive play of the game. He was carted off of the field and was said to be in significant pain as he headed into the locker room.
He got an MRI on his right knee today at Stanford and will have to undergo season-ending surgery.
The former Kansas City Chief signed a two-year deal with the 49ers in March of 2013. He signed a two-year extension in August of 2014.
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