Hannah underwent successful surgery to repair the jaw Sunday in Columbia, Mo., university officials said.
Columbia Police Sgt. Don Hawkins told the Columbia Tribune that Hawkins was leaving a bar when he was caught in the middle of a disturbance. He told police he was hit in the head with "an unknown object by an unknown person" when he tried to get away from the altercation.
Missouri Coach Mike Anderson, in a statement, said, "While our primary concern in this case is Stefhon's well-being, we will go through the process of gathering facts surrounding this incident and we will proceed appropriately."
Hannah, a senior guard, started 19 of the Tigers' 20 games this season. He was averaging 14.7 points a game and had a team-leading 105 assists. Missouri is 12-8 overall and 2-3 in the Big 12 Conference.