Crawford is eligible to seek a medical hardship waiver and could return for a fifth season.
"Drew's situation is similar to (redshirt freshman guard) Tre Demps' a year ago," Northwestern coach Bill Carmody said in a statement. "Drew aggravated a previous injury in early September and attempted to play through it, but it just hasn't responded as we all would have liked.
"While it obviously hurts to lose a player of Drew's caliber, it provides an opportunity for his teammates to step up and contribute."
Crawford was averaging 13.5 points in 10 games this season. He averaged 16.1 points and was an All-Big Ten third-team selection last season. He has scored 1,418 career points and ranks 10th in school history.