The Italy international moved to Eastlands in Aug. 2010 from Inter and, despite glimpses of his potential, has struggled to establish himself as a regular under Roberto Mancini.
Speculation over a return to Serie A intensified after a training ground bust-up between Balotelli and his manager but Galliani denies that any talks have taken place.
"The president [Silvio Berlusconi] is right, we have never spoken about signing Mario and I don't think he is for sale," he told Sky Sport 24.
Galliani hinted, however, that reports of the club's interest in bringing Ricardo Centurion to San Siro could be on the money.
The 19-year-old midfielder is currently playing for Racing Avellaneda in his native Argentina and has been linked with moves to Italy in the past, with Napoli and Inter both reportedly interested, as well as Portuguese outfit Benfica.
Galliani did not confirm any interest on Milan's part but did suggest that the team would be looking to bring in young players as they look to build a squad for the future.
"Centurion? The Milan of the future will be young, so let us see what happens," he added.
The Rossoneri official was firmer, however, on the chances of signing Cagliari defender Davide Astori, declaring: "Cagliari will not sell Astori."
Follow GOAL.COM on 