Green sustained the injury in the third quarter of Saturday's season-opening loss at No. 25 Stanford, a game he didn't start but entered after Hunter Johnson struggled. The senior was taken to a local hospital, but surgery is expected to be performed in Illinois, a team spokesman told ESPN. Green had 62 passing yards and 10 rushing yards in the 17-7 loss.
Green, the son of former NFL quarterback Trent Green, served as Northwestern's backup quarterback the past two seasons and appeared in nine games in 2018. He and Johnson competed for the starting job throughout the offseason.
Northwestern also lost starting running back Isaiah Bowser to a knee injury in Saturday's game. Bowser led the Wildcats with 866 rushing yards in 2018.