Campbell recently returned to Loftus Road after a successful loan spell with Ipswich, who are keen to sign him permanently, while Championship rivals Cardiff and Bolton have also been linked.
And Holloway said: "Have I rung Harry Redknapp? Yeah. Does that mean I'm going to get him? No. Am I fighting for him? Yeah. Will I get him? I don't know.
"But it's him and AN Other. There are lots of other players I could get.
"I think deals which get done you should talk about but deals that don't, you shouldn't.
"I never promise the fans anything I can't produce. I remember the Quincy Jones song The Dude, 'don't let your mouth write a cheque that your body can't cash'. That's what I don't like doing.
"I'm trying my best, the board are trying their best to add to the group and we know time is ticking."