The Red Devils are on a run of three straight defeats in all competitions, the second of which came at the hand of Michael Laudrup's Swansea side in the FA Cup last weekend.
A fourth successive loss when the Swans visit Old Trafford in the Premier League on Saturday would make this United's worst run since 1961, and their hopes of retaining their title appear all but over as they trail leaders Arsenal by 11 points.
But right-back Rangel has no doubts regarding the calibre of the United squad, and expects a fierce encounter in front of a fired-up Old Trafford crowd.
"I think United have still got a good number of superstars but things probably haven't worked out as they expected," he said.
"It's a difficult situation for them but when you have important players like Robin van Persie injured it is a difficult situation.
"They are still a top team and going to be a very difficult test for us.
"We have nothing to lose. The pressure is on them but the fact we won there last weekend probably makes this a more difficult game.
"The crowd will be even louder for them. They will be treating playing us like a cup final as they really need the win."
Swansea are 13th in the Premier League table, just four points above the drop zone and if results go against them this weekend that margin could be down to just one.
Rangel admits the Swans need to start picking up points, but feels it is the games that come after the trip to United which will be crucial as they look to pull away from the bottom three.
"We need points," he said. "We are not in a really bad position having dropped points against Villa, Stoke, Norwich, teams we should have beaten.
"It won't be the end of the world if we go to United and lose as we are playing away and they are fighting for the top four.
"It is not a worry but after the United game we could be a point point off relegation.
"We have got a good enough squad. There are 18 games to go and we have to be realistic, but we can get the points we need.
"We just need to start winning games at home and the Liberty has always been a fortress for us."