Van Nistelrooy allegedly confronted Nantes defender Sylvain Armarnd in the tunnel following a number of clashes on the pitch.
Match referee Kyros Vassaras however did not mention the alleged incident in his match report, so UEFA have no basis from which to act.
A UEFA spokesperson today said, "We have received the report of the referee. Nothing was mentioned in that report so no disciplinary case has been opened. That is it, full stop."
Ruud confirmed though that a confrontation had taken place, although it was out of character for him.
"I lost my mind a little bit because of an incident that happened on the pitch with their left-back," he said.
"I got a bit annoyed in the tunnel. You don't often see that with me.
"It had been something on the pitch. I don't like to mention it because it was quite dirty. It had nothing to do with football."
