Beckham's contract at LA Galaxy expires in December and he has been linked with a switch back to Europe.
"It's a difficult one," admitted Redknapp. "You would love him around your football club. As I have said many times, you couldn't get a better professional and a nicer guy.
"But he wants to play and it would be difficult because I have a lot of players here at the moment in those sort of positions, so it wouldn't be easy.
"But who knows? Let's see what happens when David's contract runs out."