The 6-foot-11 Porter was in Denver when he suffered the injury. He missed the 2018-19 season after initially tearing his right ACL and MCL in October during a closed preseason scrimmage against Southern Illinois.
Porter is the younger brother of Michael Porter Jr., the former top recruit who missed most of his lone season at Missouri with a back injury but was still selected by the Denver Nuggets with the 14th pick of last year's draft.
Jontay Porter averaged 9.9 points, 6.8 rebounds and 1.7 blocks last season as a freshman. Despite being projected as a late first-round pick last year alongside his older brother, he returned to the Tigers for his sophomore season after testing the NBA draft waters.
He is ranked as the No. 3 center and No. 24 player overall in ESPN's rankings for this year's NBA draft.
Knee problems have been an issue for the Porter siblings in recent years. Bri Porter, Jontay and Michael's sister, retired from basketball before last season at Missouri after suffering her fifth ACL tear.
Another sister, Cierra Porter, medically retired from the Missouri women's team in June because of ongoing knee problems, but she returned in December and went on to be named SEC Sixth Woman of the Year.