The Italian striker burst onto the scene with an injury-time winner on his United debut against Aston Villa in April 2009.
The 20-year-old scored a further four goals for Sir Alex Ferguson's side but his first-team chances have been limited, a situation he admits has been frustrating.
"When I had my debut it was great but then I did not have the chance to play every game," Macheda said on Thursday.
"When I got on the pitch, I tried to do my best and it wasn't easy.
"I was only 17 then and I knew I could not play in every game. It has been difficult, but I don't want to think about the past.
"Now I am here and I want to do very well here. I had a tough time. I didn't get on the pitch many times but it is a good experience.
"You have everything to learn about bad things as well so I take it as an experience and of course I need to step up to become a real player.
"Now I am young and I need to step up to become a big player. That is what I am looking for."
Several United academy graduates have gone out on loan in recent times, honing their skills and subsequently becoming key first-team players.
Tom Cleverley and Danny Welbeck are two such examples and players Macheda wants to emulate.
"I hope to do the same as them because they had loan spells for one year and it worked well for them," he said. "I hope it will do for me as well.
"When I spoke to [Ferguson] about going on loan he agreed with me. I am 20 years old and I need to get more playing time.
"It is not easy here but there is a bit more chance to play here than at United. He agreed with me and we did this choice, but I don't know about my future.
"My future is not important now. The important thing now is QPR for me and I am looking forward to doing well here. Then we will see and talk about my future."
Macheda has made 15 starts and 18 substitute appearances for United and spent the second half of last season on loan with Sampdoria.
The Italian could not prevent Samp suffering relegation to Serie B, but does not fear a similar fate with QPR.
"No, no, no, I don't worry," he said. "I couldn't help them stay in Serie A because the problem was another thing. The team did not work well and there was another situation different to here.
"In Italy everything is difficult and I never really played as well."