The 29-year-old former England man's massive £90,000-a-week wages are a huge stumbling block.
Redknapp said: "Would he have to put football ahead of wages? Oh yeah. But I like Joe.
"I wouldn't say to you that I wouldn't sign him, because I'd be lying. I'd love the chance to work with him again, because I think he's a talent and a great lad.
"He's a smashing boy who gives everything every time he plays.
"I just think if I could get him at it again and get him playing he could still do it.
"I signed him when he was 11 at West Ham. I watched him grow up. He was the best young footballer I've ever seen.
"I've never seen anyone who could come anywhere near him.
"Could I get him back to where he was? I think so, yeah."