The Spurs centre-back is currently sidelined with the groin injury that he underwent surgery on over the summer.
"He's had the injection but it doesn't seem to have done the trick really," Redknapp said.
"I don't know if he can have another operation, he's had so many. I don't know what the next step is really.
"It's a shame, he's such a good player. When he's fit he's fantastic for us but he is struggling a bit at the moment again.
"There's no light you can see. With a broken ankle or whatever at least you know what you're dealing with. But these injuries can drag on forever."