Red Devils invite Posh youngster
The 17-year-old winger will participate for the club in the Milk Cup this weekend, and is hoping to catch the eye of United's scouts.
Day follows in a long line of London Road youngsters who have spent time with The Red Devils, including Ryan Semple, Mark Coulson and Adam Fry.
Posh manager Barry Fry confirmed United had reqested the servicers of the winger, and that the club have allowed him to link-up with the Premiership champions.
"I am pleased to report that I have let our young 17-year-old talented left-winger Jamie Day follow in the footsteps of other Posh players by allowing him to go to Carrington to train with the Manchester United youth squad this week," said Fry to the club's official website.
"I spoke to Jamie on Wednesday and he is really enjoying it and it can only help his development.
"Manchester United have asked permission to take him to the Milk Cup at the weekend and I have agreed to their request."