Mark is expected to apply for a medical redshirt after the season so he can play in 2014.
Mark ran for more than 1,000 yards and was an All-America punt returner in 2012. But he has played in only one full game this season -- on Oct. 5 against Ohio State, when he ran for 60 yards on 17 carries in a 40-30 loss. He suffered the broken ankle the following week at Wisconsin. He also played briefly in the opener at California but was held out for several weeks because of a leg injury.
Northwestern, which plays host to Michigan on Saturday, has been hit hard by injuries, especially at running back. Redshirt freshman Stephen Buckley underwent knee surgery after getting hurt in the Wildcats' 27-24 loss at Nebraska. He is expected to return sometime next spring or summer.