The 22-year-old was a part of Preston's promotion-winning season last campaign and played in the play-off final victory over Swindon Town at Wembley in May.
He told Preston's official website: "I'm delighted to be back, it's good to eventually come back and I'm glad I'm here and hopefully I can start playing some games.
"I think everyone knows it was supposed to happen at the start of the season after a good end to last season but various things stopped it but I'm happy to be back now.
"It's great to be around the team at Manchester United, they are the biggest Club in the world, but at the end of the day, I'm 22-years-old and I have to think about myself a little bit and I need to be playing first-team football. I get to do that now in the Championship, which is a great league to play in."