Penn had missed four straight games before he came back and played 24 minutes in a loss to Texas Tech last weekend. But he was on crutches again for the Cowboys' 97-76 win over Oklahoma on Saturday.
OSU coach Travis Ford says Penn is "done for the year ... [and] preparing for next year already." The freshman had started 15 of Oklahoma State's first 18 games this season and was averaging 7.8 points and three assists.
Ford says Penn will not need surgery.
"It just didn't respond well," Ford said. "It's to the point now where we want him to be one of the best point guards in the league next year, so we're going to try to get him prepared for that and not take any chances."