The young Italian striker joins the South Yorkshire side after scoring five goals in 36 appearances for the Red Devils since joining from Serie A side Lazio when he was 16.
Macheda has made 36 appearance for the United first team, scoring five goals since joining from Lazio as a 16-year-old. Now 22, Macheda trained with his new teammates on Sunday and Monday and could feature against Watford on Tuesday.
Doncaster manager Paul Dickov has called the transfer a coup for his side and is hoping for a healthy goalscoring return from the Italian.
"We've got him for an initial month with a view to extending it to the 93 days, which is the maximum," Dickov told BBC Radio Sheffield. "I know from speaking to Sir Alex Ferguson and David Moyes he's a top quality player, and David knows we'll look after him and keep him informed on his progress.
"We had a little nibble at him before the season started, but it wasn't to be then.
"Hopefully he'll add goals. He's been to big clubs on loan but not really played for them, and he's very hungry to get his career back on track. It's been a frustrating couple of years for him and he's keen to hit the ground running."
Macheda spent the latter part of last season on loan at Stuttgart after previously being sent out to Sampdoria and Queens Park Rangers.
He is most known among United supporters for his 90th-minute wonder goal against Aston Villa, which swung the 2008-09 title in the Red Devils' favor.