The man, whose name was not released, told the Bild newspaper he was eating Friday evening at the Grill Royal restaurant in Berlin and was told by his waiter his $134.66 bill had been covered by Clooney, who had been dining with friends at the next table, The Local.de reported Monday.
The waiter told the man Clooney was concerned he and his friends had been rude while the man was trying to eat.
"That's not true at all. They had behaved in a very cultivated manner. I was stunned," the man said.
The diner, who said he did not recognize Clooney at first, said he left his business card for the actor in the hopes of eventually returning the favor.
Clooney is in Germany filming scenes for upcoming film "The Monuments Men."