The 49ers elevated Willis from the practice squad to the active roster Saturday, Cam Inman of The San Jose Mercury News reports.
Willis was unable to make the 49ers' 53-man roster at the end of training camp, but he opted to stick around on the practice squad. With George Kittle (hamstring) ruled out for Sunday's game against the Rams, Willis will serve as the 49ers' No. 3 tight end behind Eric Saubert and Jake Tonges.