From the Timberwolves site:
Minnesota Timberwolves forward Al Jefferson underwent successful surgery today to repair a torn anterior cruciate ligament (ACL) in his right knee. The procedure was performed this morning by Dr. David Altchek at the Hospital for Special Surgery in New York, N.Y. Jefferson suffered the injury during the Timberwolves Feb. 8 game at New Orleans and will be sidelined indefinitely as he begins rehabilitation.