The promising Italian lauded his Old Trafford team-mate for his skills and advice, but indiscreetly described him a 'coatto' in an interview with Gazzetta dello Sport.
The term means working class and vulgar, with the closest colloquial translation being 'chav'.
Face to face: Macheda (left) and his United team-mate Rooney
Who's a chav? Rooney this week
Rooney is no stranger to criticism in light of his off-the-pitch behaviour, but he might have expected more solidarity from a player taken under the England striker's wing at Old Trafford.
'Rooney is a really great person, he always gives me advice. But, as we say in Rome, he's a bit of a coatto.'
The 19-year-old is with the Italy Under 21 side ahead of a double header against Romania and he has caught the eye after an impressive start to the season.
Sir Alex Ferguson has involved the striker five times already this season and clubs in Italy are keen to take him back home.
Lazio have already been linked with a move and today Juventus have been tipped to make a bid that could even see Italy keeper Gigi Buffon offered in exchange.
Speaking after hearing of Lazio's interest, he said: 'I want to improve in Manchester, when I'm more mature I'll be able to make choices. The rumours about Lazio please me but I don't think I will go.'
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