Redknapp managed Ferdinand while they were both at West Ham, and despite admiring the former England captain he says he is not a player Spurs are looking to sign.
"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?"
Redknapp has also been heavily linked with another bid for Bolton Wanderers and England centre-half Gary Cahill, but says defence is not an area he is currently looking to strengthen after the return to fitness of Ledley King.
"I'm not looking to strengthen in defence, really. We are strong in defence. We have [Michael] Dawson, King, [William] Gallas, [Younes] Kaboul and [Sebastien] Bassong," added Redknapp.
"I went for Cahill because at the time I couldn't see Ledley being fit and because William Gallas had a calf strain."