The Blades were due to entertain the Tigers in their final home game of the year, but it has now been postponed.
Hull City informed the EFL that it would be unable to fulfil the fixture at Bramall Lane due to a number of positive Covid-19 cases in their squad.
Hull, whose Boxing Day clash against Blackburn was postponed just over two hours before kick-off, said: "Our match at Sheffield United on Wednesday 29 December has been postponed due to the Tigers having an insufficient number of players available to fulfil the fixture.
"The club has worked hard to ensure it has been able to play the game. However, taking into account the injuries and positive Covid-19 cases in the squad, we do not have the required numbers for the match to take place."