Porter's brother, Michael Porter Jr., announced last month that he would leave the Tigers after one season and declare for the draft.
Jontay was the No. 11 player in the Class of 2018 and reclassified to join his brother at Mizzou. He averaged 9.9 points, 6.8 rebounds and 2.2 assists this season.
The Porters' father, Michael Porter Sr., is an assistant coach for the Tigers.