After getting a MRI at New England Baptist Hospital, the diagnosis was confirmed by team doctor Brian McKeon.
The Celtics said the star point guard would have surgery to repair the injury at an unspecified date.
Rondo returned to TD Garden in the third quarter in the warmups he was wearing when he left during pregame warmups, walking with a slight limp but no crutches. He walked down to the Celtics locker room on his own power.
Rondo came to the Garden Sunday morning for his normal pregame shootaround but went back in for more treatment on the knee as the pain continued in his right knee. He was taken to the hospital with a preliminary diagnosis of a hyperextended knee.