Lewis suffered a torn ACL during Sunday's preseason opener and will now miss the remainder of this season, NFL.com's Ian Rapoport reports.
Lewis was forced out during the third quarter of Sunday's game, when he was the second signal-caller used in wake of Colin Kaepernick (shoulder) being sidelined. However, now that his season has already come to a close, rookie Jeff Driskel should see more reps behind Kaepernick and Blaine Gabbert.