Harry Redknapp's men, currently bottom of the table, are desperate to reduce their seven-point gap to safety, while United are closing in on a 20th league title.
And Mbia, whose side saw a five-game unbeaten league run come to an end in a 4-1 defeat at Swansea, is under no illusions about the challenge that lies ahead.
"I have confidence in what we can do because everyone is together, everyone wants to fight for this club," the 26-year-old told the club's official website.
"We are desperate to stay in the Premier League. Every game for us now is going to be a battle, a fight.
"Personally, I am feeling very fresh. I just want to do the very best I can for the club every time I am on the pitch and I am looking forward to Saturday.
"It's going to be a big game for us and it is very important that every player gives 100 per cent for themselves, for the club and for the fans who are right with us.
"We have big respect for Manchester United but we will give everything we have in this game. And then we will see what will happen.
"This game on Saturday is very, very important. After the 4-1 result against Swansea all of us know exactly what we want to do and what we need to do in this match."