Middleton sealed the deal on Tuesday evening and joins six other United players under contract for the 2019-2020 season.
Midfielder Nicky Wroe, meanwhile, has terminated his contract by mutual consent due to travelling issues and work commitments.
CONTRACTED FOR 2019-2020
TERMS AGREED FOR 2019-2020
INVITED BACK FOR PRE-SEASON 2019-2020
RELEASED WITHOUT OFFER
LOAN PLAYERS RETURNED TO PARENT CLUBS