He said: "About Liverpool, (I'll talk) on Friday. I played Luton in the FA Cup not thinking about United. I needed energy today, fresh legs. I know how tired, you don't know how exhausted some of our players were today.
"To play just three days after. Normally in the Champions League, when you play on Wednesday, all the countries in the world except here they allow you to play Saturday. We played Sunday. I needed fresh legs, we were fortunate, lucky to score two goals early and then Erling helped us a lot."
Asked about the schedule, he laughed: "No, it is not the Premier League, it is the broadcasters and they all say the same answer, we pay a lot of money so shut up!
"We have injuries with Jeremy (Doku) and Jack (Grealish), we need to be fresh. I know Phil (Foden) how he runs against United, Phil has the dynamic to play, Bernardo (Silva) as well. I spoke with them, they said many things, but they said 'Pep, I'm so tired'. Okay, maybe the last 30 minutes if the situation is difficult you can do it."