Simpson has been playing in United's pre season games and on Saturday played in the game against Espanyol, but is not likely to get many games as he will be behind Wes Brown and Gary Neville in the pecking order.
The 21 year old has been out on loan before, he has spent time with Belgian side Antwerp and in the Championship with Sunderland and Ipswich.
He has also made appearances in United's first team.