Prohm had told ESPN on Thursday that if McKay could get through the week without any further incidents, he would return for the Cyclones' game against Texas.
McKay, the Big 12's reigning defensive player of the year, has missed two games after the senior was suspended last Thursday for an incident that happened during practice.
The No. 14 Cyclones beat Oklahoma State and lost to Texas Tech without McKay, who is averaging 12.0 points, 9.0 rebounds and 1.7 blocks.
Prohm told ESPN that he issued the indefinite suspension because he wanted to see how McKay, whose tweet last Friday suggested that he'd miss just one game, would handle it.
ESPN's Andy Katz and Myron Medcalf and contributed to this report.