The Italian striker has joined QPR on loan for the rest of the season and made his debut as a substitute in the home defeat to Norwich.
Macheda also had a spell on loan at Sampdoria last season, but Warnock does not believe that the 20-year-old no longer has a future at Old Trafford.
"He's a big fan of him is Sir Alex," Warnock told a press conference.
"He doesn't want to let him go. He thinks there's something there in the player and he's no thoughts about a sell-on if we'd like to buy him.
"He doesn't want to let him go and Sir Alex doesn't do that with many, unless he thinks there's something there."
Macheda burst onto the scene as a 17-year-old with an injury-time winner on his United debut against Aston Villa in April 2009. He has scored a further four goals for Ferguson's side but his first-team chances have been limited.
"They've got some great players and for a 17-year-old to try and get established, irrespective of what he did on his debut, is almost impossible with what they have," Warnock said.
"This is a chance for Kiko to try and get into the team."
Macheda has made 15 starts and 18 substitute appearances for Unitedso far.