Goals from Juan Mata and Marouane Fellaini gave United a 2-0 win in the first leg.
But Mourinho admits his side still have a lot of work to do if they are to lift the EFL Cup this season.
“I know that it’s going to be hard. Let’s see what happens," said Mourinho.
Jose Mourinho was speaking ahead of Manchester United's match against Hull tomorrow
Manchester United hold a 2-0 lead going into the second leg against Hull
"In this moment, we have a 35 per cent chance to win the EFL Cup.”
Along with the EFL Cup, United are still competing in the FA Cup and Europa League.
And Mourinho fears a fixture congestion could affect his side later on in the season.
Manchester United's predicted team to face Hull in EFL Cup
Tue, January 24, 2017
Express Sport brings you Manchester United's predicted XI to face Hull in the EFL Cup semi-final second leg
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Who will Jose Mourinho start against Hull in the EFL Cup semi-final second leg?
“It’s nice to win a competition but I don’t think it’s crucial to do well after that," he added.
“We go competition by competition and match after match. It’s going to be really difficult.
“I have a board with all the matches and possible matches on my office wall and when I look at it the image is quite complicated.”