Petrucci, who is getting his first taste of first-team football, is one of two Reds at the club with centre-back Scott Wootton completing his second stint at London Road.
"The ones I brought in have made a difference," commented Darren Ferguson to Posh Player. "Wootton and Petrucci were a no-brainer coming from there [United] because they are good players."
The creative midfielder added on Peterborough's official website:" I am very happy. I only signed for a month in the first place because it was my first loan spell. I didn't know what to expect.
"However, since the first few days, I realised that I wanted to stay for longer and I am very pleased to be here until the end of the season."