Ferdinand's showings have come in for criticism from certain quarters following his move from Manchester United, with Redknapp's men conceding 13 goals in the top-flight.
Only Everton have shipped more, but Redknapp feels a lack of continuity in his starting XI has hindered his defence from gelling.
Redknapp brought in a number of signings over the close-season but has suffered badly with injuries, something that has proved a frustration for the former Tottenham boss.
Asked if he agreed with some of the comments on Ferdinand's form, he said: "No, I don't think it's fair.
"We've been a bit open and I think teams have got at our back four a bit easily but it's been difficult because I've brought in some midfielders to the club and they've never been fit.
"I've got no problems with Rio, none whatsoever.
"It's been difficult for everyone because no-one's been fit. Sandro is a top player but I've not seen him fit, [Jordon] Mutch has been injured.
"Leroy Fer is getting close to top gear, Joey Barton's been injured for weeks. We've not had the chance to have a settled team."
Adel Taarabt is another of Redknapp's side to see his playing time limited this term, with the Moroccan only making one start and substitute appearance in all competitions due to an ankle injury.
The attacking midfielder spent time on loan at Milan last season but Redknapp does not believe the Italian giants have retained their interest in the player.
Asked whether Milan were keen to sign Taarabt, Redknapp explained: "They don't seem to be no.
"The first thing he needs to do is to get fit and start playing football here. We want Adel to be fit to play for QPR.
"I don't know whether he's got the green light to leave in January, he had the green light to leave in the summer but Milan didn't come in for him. He's always had the green light if someone wants to pay the money the club want for him.
"You've got to have plenty of patience with Adel. I get on well with him, we just need to get him playing."
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