Loftus Road will host a potentially pivotal match in the relegation battle, with Rangers seven points adrift of safety and Wigan above the bottom three on goal difference alone.
Successive defeats to Aston Villa and Fulham have left QPR in a dire position, but Redknapp wants his team to share his conviction that they can stay in the top flight.
"When I stop believing, the players will stop believing. If I send out the wrong message they'll down tools, thinking we've had it," he said.
"I don't feel we've had it. I couldn't tell you the pleasure keeping QPR up would give me. It would be fantastic.
"We have to keep going - we've got to beat Wigan. There's nothing else for it, we have to beat them.
"Nothing else but a win would be any good to us. We need to win and keep winning. We need to win four or five games - it's a tall order but not impossible.
"But if we don't win on Sunday we won't give up because there'll be six games left and we could still win all six. You don't give up, you have to keep going."
QPR have spent heavily under chairman Tony Fernandes, who has insisted the club will be financially secure even if they are relegated.
Those players on large salaries such as Christopher Samba and Loic Remy will depart, while the future of Redknapp himself will be shrouded in doubt.
Fernandes stated on Thursday night that he wants Redknapp to stay even if Rangers slip into the npower Championship, a prospect that is agreeable to his 66-year-old manager.
"We've never discussed relegation. We've never thought about relegation. We're positive and still believe we can get out of it," Redknapp said.
"We haven't looked at next season, players or anything else. We still have a job to do this year.
"It's up to the owners and the chairman if I stay on. I'm happy here, it's a good club with good people. I love it here.
"If Tony Fernandes wants me to stay I'll stay. I've not been one for moving around that much.
"If I could have four years at QPR I'd be delighted, but I'd have to be successful to stay here. If I can do well here I'd love to stay."
Samba, the Congo centre-back signed for £12.5million in January, will have a key role to play if QPR are to escape relegation.
Two errors on Monday night gifted Fulham a 3-2 win at Craven Cottage, but Redknapp has leapt to the defence of the 29-year-old, who has been the subject of abuse on Twitter.
"Samba had a nightmare to be fair, but he was absolutely brilliant when we won at Southampton," he said.
"It was one of the best performances from a defender I've seen for years. He's a top player who could play for any side in the top four.
"He had a bad night against Fulham, but he's not the first defender I've seen make mistakes. On Sunday I'm sure we'll see the Samba we're used to seeing."