Chelsea go to Old Trafford with United to be led by caretaker manager Ruud van Nistelrooy. Ruben Amorim was named permanent manager of United on Friday.
Maresca said: "First of all, all the best to him. If the people in charge took that decision it is because they think it's the correct one. All the best to him and all the best to Manchester United.
"I haven't spoken with Ruud. I will give him a big hug on Sunday before the game. We expect a tough game.
"First of all, a fantastic guy - very humble and professional. Unfortunately I shared with him a time where he was already finished but even with that, you can see how good he was. We had a very good group of human beings with Malaga at the time so it is always nice to remember that moment."
He added, "We didn't win there since 2013? Hopefully it is a good time. That shows how difficult that stadium is; not only for us but for every club."