Serie A's disciplinary tribunal said in a statement on Tuesday that Gattuso "left the technical area and made an intimidating remark to a player of the opposing team" during the 2-1 win at Chievo on Saturday.
Gattuso, ordered from the touchline, was fined 15,000 euros (12,842 pounds) and given a warning. Milan, third in Serie A, face fourth-placed Inter at San Siro on Sunday.
Atalanta coach Gian Piero Gasperini, however, was banned for one game for pushing a Sampdoria official in the tunnel after being sent off in his team's 2-1 win on Sunday.
Gasperini, dismissed for angrily protesting a penalty, said after the game that he had merely "nudged aside" the official and that Sampdoria had made a "song and dance" about it.
However, on Monday, he apologised after a video of the incident was published on several websites.
(Reporting by Brian Homewood; Editing by Toby Davis)
