But he rated him so much he insisted on a massive buyout clause in his deal with QPR.
Redknapp said: "In the end it was difficult and if I'm honest about it, I didn't really want to get rid of him.
"I was scared to let him go because I always thought he would come back to haunt me or bite me on the backside. The chairman, Daniel Levy, got a big sell-on clause as part of the deal because we felt he could go on.
"I know we got a big sell-on agreement because we were always afraid that he could progress. But he basically wasn't playing and he always wanted to play and wasn't in the team at Tottenham.
"I had a lot of good players in the middle of the park and I had Rafael van der Vaart coming in.
"It was difficult for Adel so we let him go, took the chance and got a big sell-on in case he did go on to do what we thought he might do.
"Okay, he's a bit of a fruitcake - but what's he worth now? I don't know. In the summer they were talking big money but now you're probably not talking the same figures.
"But his valuation will vary. It depends because if he has a run when he's hot, it might be time to sell him.
"He is so unpredictable. You'd love to have him even on the bench because he can come on and turn the game. He came on against Arsenal for us the other year and nearly won the game. Against Burnley in the Carling Cup he turned the game.
"He can do anything, believe you me. When he picks that ball up and runs at you, he has fantastic ability.
"I liked him as a lad, he's not a nasty boy. I think he's a bit of fruitcake but there's nothing nasty about him."