Redknapp also believes that manager Jurgen Klopp had a big impact on Oxlade-Chamberlain's football, with the player looking much better than when he first joined from Arsenal late in the transfer window.
"I wasn't sure about the move for him to start with and I was wondering how he was going to do, but he has surprised me," said former Liverpool midfielder Redknapp.
"I looked at him at Arsenal and it was like he was treading water and going nowhere, but under Jurgen Klopp I am seeing a completely different player. I am seeing he is fit, with a great attitude and wanting to win tackles.
"It's probably unfair to question how he was coached under Arsene Wenger but I watched him play and I didn't feel he developed for years. It looked like he was standing still. I feel a lot of players at Arsenal are in a similar situation.
"You can go and sign a new contract and say 'OK, I'll be on the bench', but he has taken a risk in his career. He could have stayed at Arsenal and signed a new contract but he wanted to challenge himself and has gone to live up north and given himself a chance to play in the first team.
"He wasn't guaranteed a spot but he is in now and it will be hard to dispossess him of the shirt.
"It was a really bold move for him and one that is really paying off. Look at how much he is improving, he has got fitter, stronger, and he is a different player than he was at Arsenal."