The 64-year-old managed the England international in his youth at West Ham United but has insisted that he is not looking to bring Ferdinand to White Hart Lane.
Ferdinand, 32, has been struggling to cement a regular place in United's defence because of injury struggles and the emergence of young talent such as Chris Smalling and Phil Jones.
"I haven't even thought about Rio to be honest," said Redknapp.
"I signed him as a kid. I love Rio as a boy and a player, but it's not something we have ever enquired about.
"It's going to be difficult for him to leave Man Utd isn't it?"
Spurs made a late bid for Bolton defender Gary Cahill in the summer transfer window and are said to be readying a fresh bid for the 25-year-old, whose contract expires at the end of the summer, in January.