Serie A giants Juventus have been credited with an interest in the 19-year-old, who joined United from Lazio in 2008.
But Macheda's representative, Giovanni Bia, has insisted the forward is settled at Old Trafford.
"An interest of Juventus? These rumours are pleasant, but I think Macheda is not for sale," Bia told calciomercato.it.
"This is not the time to talk about the market. Federico is only thinking about the Under 21s and Manchester United.
"He plays in a great team and he would think two thousand times before leaving, even if the club ever thought about selling him.
"Sir Alex Ferguson always speaks well about him and declare him non-transferable.
"It's something normal that clubs take an interest in him also because he is very young.
"But he is happy in Manchester."