The incident took place in a Los Angeles hotel Thursday night. USC and Arizona met Friday in the tournament semifinals.
USC Athletic Director Pat Haden announced the suspension after talking with O'Neill.
"I expressed my disappointment in his involvement in an incident last night in which he and his wife engaged in an argument with a supporter of another school," Haden said in a statement.
Haden said additional discipline was imposed, but did not say what it was.
"I want to apologize to my team, our university and our fans for my involvement last night in an incident with a fan," O'Neill said in a statement. "I understand my behavior as the leader of our team was unacceptable. I used poor judgment and put myself, my team and USC in a bad light. I regret that I have let them down."
O'Neill is in his second season as coach of the Trojans, having previously been an assistant under Lute Olson at Arizona.
O'Neill was Arizona's interim coach during the 2007-08 season while Olson took a leave of absence and then was named as Olson's successor. Olson, however, decided he would return to coaching for the 2008-09 season and O'Neill eventually left the school.