Fortson suffered a right knee injury during Sunday's 27-20 win over the Raiders, Charles Goldman of AtoZSports.com reports.
The tight end did not catch his only target Sunday. Fortson saw two targets on 21 offensive snaps in two previous games this season, making one catch for five yards and no touchdowns. The Chiefs' top three tight ends, Travis Kelce, Noah Gray and Jared Wiley, are all healthy.