Norwich snatched the Celtic striker away from the QPR boss after they matched his £5million offer.
Redknapp told the Scottish Sun: "I'm disappointed it's fallen through. I thought we had the deal.
"But that's football and I wish Gary all the success at Norwich. He's a nice boy with a nice family and I'm just disappointed that we didn't get him.
"We should have got him but we let it drag on too long and in the end we lost him.
"Had he indicated he would join us? Yeah and the deal was there to be done. But we just didn't quite get it over the line.
"That left ourselves in a vulnerable position and Norwich then came in and did the deal.
"Do I wish we'd offered more? No. We made him a good offer, it just dragged on too long getting to the offer. That's the problem.
"If we'd got to where we got a little bit quicker I'm sure we'd have done it - and we should have got it over the line.
"We're all disappointed but that's how it goes. We move on and I wish him every success."