The 6-6 sophomore wing suffered the injury in practice and had surgery this past week.
Garino was one of three players on George Washington's roster to start all 30 games last season and averaged 8.8 points per game in 26.9 minutes per contest.
In other Colonials injury news, point guard Joe McDonald sat out the team's exhibition game Saturday after suffering a hip injury a few weeks ago. Lonergan said nothing is set in stone regarding McDonald's return, but he "may try and practice next week."
George Washington went 13-17 last season and opens up Friday at home against Radford.