The London club are rooted to the foot of the Premier League table after picking up just four points from their first seven matches.
Redknapp bolstered his squad with a host of close-season signings following QPR's promotion via the Championship play-offs, but new faces such as Jordon Mutch and Sandro have been hampered by injuries as they aim to settle in at Loftus Road.
Sandro, who also played under Redknapp at Tottenham, managed to play 67 minutes of a 2-0 defeat to West Ham on Sunday, while Mutch was introduced for the last 12 minutes after missing the previous weekend's loss to Southampton.
"It's been difficult," said Redknapp. "People like Jordon Mutch and Sandro, that I bought in, at the moment have not managed to put two games together and it's been a problem for us.
"With a few of them, we've really got to get them fitter.
"I've put a lot of faith into Sandro, but unfortunately he's had an injury and we need to get him fit, because when he's fit, he's a fantastic player. I had him at Tottenham, he was an excellent player, but at the moment he's short of fitness.
"The doc comes to me at half-time [in the West Ham game] and says he can only do another 15 minutes - I need to get them fit enough to play 90 minutes.
"There's a little group who at the moment are struggling, I think, on their fitness, because they've had injuries and missed training. We've got to get everybody fit and ready to go."
