Photos in weekly glamour magazine Oggi, which was released on Wednesday, appear to show a nocturnal kiss between Pato, 21, and Barbara Berlusconi, 27, while others show Milan vice-president Adriano Galliani entering the striker's home.
Despite his tender years, Pato is already a divorcee, having seen his marriage to Brazilian actress Sthefany Brito end a year ago after less than 10 months.
The Brazil international has struggled at times to break into the Milan first team this season due to injury problems and competition from Zlatan Ibrahimovic, compatriot Robinho and Antonio Cassano.
His relationship with Ms Berlusconi, the heiress to the club her father - the Italian Prime Minister - owns, has become the talk of the footballing gossip channels in Italy.
Pato also previously dated Miss Brazil 2010, Debora Lyra.
Pato 'pictured with Berlusconi's daughter'
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