With the west London side falling six points behind 17th-placed Aston Villa, the R’s can ill-afford to any more slip-ups in the relegation battle.
QPR have an impressive record against the big sides at Loftus Road – Chelsea, Manchester City and Tottenham were all held to goalless draws this season – and Mbia admits that the Hoops need to be at their best for the visit of Sir Alex Ferguson’s men.
“This game on Saturday is very, very important,” Mbia told QPR’s website.
“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.”
He added: “I have confidence in what we can do because everyone is together, everyone wants to fight for this club.
“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.”