Earlier this week, Redknapp had been confident of bringing Hooper to Loftus Road after QPR finally had an offer accepted by Celtic.
However, QPR's failure to finalise personal terms with Hooper opened the door for the player's long-term admirers Norwich to step in with a bid.
Norwich saw a January transfer window offer rejected by Celtic, but agreed a fee in the region of £5.5million for the former Scunthorpe forward.
Hooper passed a medical with the Premier League club and is expected to sign a four-year contract at Carrow Road.
Redknapp has described missing out on Hooper as a "huge setback" and has lamented the delay in QPR trying to conclude a deal.
"It's very disappointing because I felt there was a deal to be done there but maybe this is a lesson learnt for us," said Redknapp in the Daily Telegraph.
"You have to get transfers like this done quickly. If you take your time you are always open to the risk of somebody else coming in and that seems to be what's happened with Gary Hooper.
"It's definitely a huge setback for us because I thought he would have been a fantastic signing for us."