The 20-year-old Italian, who has started two League Cup matches this season and made three Premier League appearances as a substitute, also spent time on loan at Sampdoria last season.
“There is a lot of competition at Manchester United, there are some very good strikers there,” Macheda told QPR’s website (www.qpr.co.uk).
“But I am still young and I need to get more experience in the Premier League.”
QPR manager Neil Warnock said: “This is a great opportunity for both parties. Federico is not getting a regular game at United quite obviously because of the quality of the squad they’ve got.
“Everybody in the league is in envy of what (manager) Sir Alex Ferguson has there … but I believe this can really work for us because he is positive and always in and around the box. He can finish too.”
Macheda hit the headlines when he came on as a substitute to score a superb injury-time winner on his United debut against Aston Villa at Old Trafford in April 2009 but his opportunities have since been limited.
Rangers, who are fourth from bottom, host Norwich City later on Monday (1500 GMT).