Hawthorn football manager Jason Burt confirmed the news on Sunday, after Birchall suffered the injury in a mid-air collision with Adelaide forward Tom Lynch.
“Grant had scans last night which unfortunately confirmed a fracture of the jaw,” Burt told the club’s website on Sunday.
“He will have surgery today and we will have a better idea on his timeline for return following that. At this stage, it is likely to be somewhere between three to four weeks.
“It’s a disappointing result for Grant so early in the season, but he’ll be doing everything he can to return to the field as soon as possible.”