The 25-year-old leaves Sky Bet Championship club Birmingham City and walks straight to the side for tonight’s Sky Bet League One fixture with Fleetwood Town.
The loan is initially for seven days, so it would include Rotherham United’s visit on Saturday.
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It comes after United postponed Saturday’s trip to Wigan Athletic following a Covid outbreak that left them without a senior goalkeeper.
Head coach Karl Robinson said: “He was one of those we knew, he played league football.
“We looked at a number of different options, but thanks to Bow (Lee Bowyer, Birmingham manager).
“We called a bunch of managers and it was about finding one who was available and willing to drop a hat to say yes.
“It was 9pm last night, he’s here and he’s ready and eager to go.”
Trueman’s only match at Birmingham this season was in the Carabao Cup first round in August, with the scorer behind Matija Sarkic and Neil Etheridge in the pecking order.
He joined the Blues in his youth and played 44 senior games during his career, including 13 in the league.
Trueman faced United three times last season, on loan at AFC Wimbledon and then Swindon Town.
He was in front of goals for a 1-1 draw in the Carabao Cup first round at Kassam Stadium in September 2020, won by the U on penalties.
The stopper returned to Grenoble Road for a 2-0 loss to Sky Bet League One on Boxing Day.
He was then sent to Swindon on an emergency loan in March and began their 2-1 home loss to United. The arrival of Trueman puts an end to Karl Robinson’s search for a goalkeeper, with his four oldest players in the post all unavailable.
Simon Eastwood was one of seven players to test positive, with 18-year-old Kie Plumley also isolating himself as a close contact.
Jack Stevens is recovering from glandular fever and Mackenzie Chapman is loaned to Banbury United.