The Italian playmaker recently became the 30th United youngster to move to Belgian side Royal Antwerp on loan as part of an agreement between the two clubs.
"I am at the age where I need to play. Reserves football is fantastic when you are young but for us, me especially, I played there for a few years and won everything every year. I needed that step up. I couldn't do more than we have done already," he told United's official website.
"I think it's not easy for [manager] David Moyes because he's just arrived and needs to have more focus on the first team. It's understandable but I need to think about myself and try to play as well as I can. Hopefully, he will see that and I will come back.
"You need to believe all the time - otherwise there is no point to play football, you know. If you don't believe in yourself, it is better not to play. I hope I can come back to United and play for the first team."
Petrucci joined United as a trainee from Roma in 2008.