The 6-foot-10 Porter, considered the possible No. 1 overall pick in June's NBA draft, was injured two minutes into the season-opening rout over Iowa State. He had two points and two rebounds in two minutes before leaving the game.
Porter didn't play against Wagner on Monday night, and also wasn't on the bench the entire game. A school spokesman told ESPN he was in the trainer's room, watching the game and icing his leg.
The Tigers lost 77-59 to Utah on Thursday night in Salt Lake City.
Afterward, Missouri coach Cuonzo Martin was asked by reporters there if Porter's status is day-to-day.
"I think so," he said. "I'll find out more when we get home."
Information from ESPN's Jeff Goodman was used in this report.