The Reds were involved in a unexpectedly hard-fought contest against Notts County in the Capital One Cup, eventually prevailing 4-2 after extra-time.
And the Belgian goalkeeper does not believe the Anfield outfit will suffer a hangover following the gruelling tie, and says a tough pre-season campaign means they are prepared to play three games in a week.
"We are professionals and we worked really hard in pre-season to get fit for the start of the season so that won't be an issue," the goalkeeper told the Liverpool Echo.
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"It will be a huge experience for me against United and I always look forward to these types of games. It's going to be a big one and we will try to win the game. We will make sure we're ready for Sunday.
"We have to look at ourselves rather than focus on who we're playing against."
Mignolet is happy to have progressed to the next round of the Capital One Cup, though admitted Liverpool were culpable of switching off and allowing Notts County back into the game.
"We're just relieved to have won the tie," Mignolet continued. "We wanted to get through to the next round and in the end we did that.
"Obviously when you lead 2-0 at half-time you hope that things are going to go a lot more easily for you and that's what happened tonight. That was disappointing and so were the injuries we suffered.
"We made it difficult for ourselves in the second half. I wouldn't say it was complacency but even if you lead 2-0, no matter who the opponent is, the game is not over.
"We tried to score a third goal but that didn't work out and then they got a goal from a set-piece which changed the game.
"We have to learn lessons but we're into the next round and that's the most important thing. We want to do well in this competition and maybe further down the road we will look back and take the positives from this game.
"We still have a chance to win the cup. At one stage tonight it didn't look like that would be the case."