The Blades are a part-time team in the Women’s Championship so some players cannot make it to Manchester in time.
The Continental Cup kick-off time was agreed at the start of the season.
United’s attempts to delay the kick-off last week were turned down by City because they had already sold tickets and booked stadium staff.
Sheffield United, who are competing in the second tier for the first time this season, accepted City’s reasoning and say they have learned their lesson.
They only contacted City, who are second in the Women’s Super League and were 2016 champions, on 29 November once they knew they would be struggling for players.
City like playing games early in the evening so that they get a better crowd, but it means that visiting manager Carla Ward will be forced to play youth players instead.
Players who cannot make the game include a teacher, a student and one who works in a bookmakers.
Several players are hoping to make it to the stadium less than an hour before kick-off.
City are one of the best-funded sides in women’s football, and manager Nick Cushing can call upon a host of internationals in his squad, including England players Steph Houghton, Jill Scott and Nikita Parris.
After three games they are top of Continental Tyres Cup Group One North while Sheffield United are second bottom of the six-team mini-league.