The Hoops are struggling for form after succumbing to an emphatic 3-0 defeat by Liverpool at Loftus Road on Sunday.
QPR have the chance to move within five points of 17th-placed Southampton if Redknapp’s men can complete an unlikely victory at Stamford Bridge.
Rafael Benítez’s side are on a three-game winning streak in the Premier League, but Redknapp insists the R’s will stay positive despite the gulf in class between the two sides.
“Chelsea will be really tough,” Redknapp told QPR’s website.
“Rafa Benitez is a top, top manager and he’s gone in there – with an unbelievable squad – and got some very good results.
“They’re in great form and it’s a massive ask for us.
“We’ve got to believe we can beat them though. It’s a London derby. Who knows? Maybe we can produce a shock result. We’ll give it a real go.”
Redknapp’s assistant Kevin Bond said that QPR have had no choice but to put the disastrous Liverpool result behind them ahead of Wednesday’s fixture.
“We have put the Liverpool game behind us but it’s not forgotten about,” said Bond.
“We will try to be resilient and we will try to get nearer to people if we can.
“We didn’t feel we got near enough to people in the Liverpool game and there were too many gaps for them to work in.
“So we will try to avoid that and we’ll look to be a threat as well which is what we’ll need to be if we’re going to win the game. And that’s what we’re looking to do.”
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