A goal late in the first half from Peter Crouch, and a Jon Walters penalty late in the second sealed a vital three points for the visitors, but means the R's are now 10 points from safety, with only 12 to play for.
And Redknapp knows anything other than four wins, as well as results going their way, will mean his side will be plying their trade in the Championship next season.
"It will take a miracle now. It is almost impossible," he told Sky Sports.
"We had a go, but maybe we are short of that bit of quality needed in this league."
The former Tottenham boss pointed to the absence of Bobby Zamora and the injuries to Andros Townsend and Adel Taarabt as pivotal moments of their latest defeat.
"Zamora's sending-off a few weeks ago was a massive blow," he added.
"I liked the look of him and Loic Remy together.
"As well, with the injuries to Townsend and Adel we lost two key players today, just when we needed that little bit of luck. There was no way back from there."