Both of United's outstanding home fixtures have now been rearranged, with both taking place on consecutive midweeks.
The game against Millwall and Coventry City were both postponed because of the opposition's involvement in the Emirates FA Cup and Checkatrade Trophy respectively.
Firstly, the Lions will now visit Bramall Lane on Tuesday 28th March, kick-off 7.45pm.
Then, the fixture against the Sky Blues, will be played at the Lane on Wednesday 5th April, kick-off 7.45pm.
The Coventry game has been rearranged for the Wednesday evening, owing to City's Wembley final on the Sunday.
Tickets already purchased for the Millwall match remain valid, but should supporters require a refund then they can be returned to the Ticket Office any time prior to kick-off.