Chelsea are said to have made an improved bid for Modric after their initial £22 million offer was dismissed by Redknapp as "ridiculous", and the player has confirmed that he is eager to move to Stamford Bridge as he seeks to return to the Champions League.
However, Spurs chairman Daniel Levy issued a statement on Saturday stressing that he had made "abundantly clear" to Chelsea that Modric is not for sale and that "they chose to ignore it and then subsequently made the offer public". Levy added: "For the avoidance of any doubt, let me reiterate that we shall not enter into any negotiations whatsoever, with any club, regarding Luka."
Reports on Sunday in the English press claim Spurs could report Chelsea over the pursuit of Modric and that, even if the Croatia international issues a transfer request, he will not be allowed to leave, and Redknapp has now revealed Chelsea are not the only club to have been rebuffed in their attempts to sign the player.
"Chelsea are not the only club that have been in for him," he told BBC Radio 5 Live. "There have been other clubs - top, top clubs - but if Tottenham are looking to go anywhere we can't be selling Luka.
"We have to do something to keep him at the club. We can't afford to sell Luka Modric if we want to be a successful club."
He added: "I think we have to show him our ambition, which we will do. If we can add one or two good players to our squad there's no reason we can't have another great season, so Tottenham could be a great club for him to stay with for the next few years. That's what we're hoping for."
With Spurs fans likely to be unhappy that one of their key stars has expressed his desire to join their London rivals, Redknapp has moved to defend Modric.
"He's a fantastic lad," he said. "You'll never meet a better lad than Luka. I suppose he's seen a massive contract and the chance to win the Premier League and play in the Champions League and that's what he wanted, but we want that as well.
"We want to get back in the Champions League and we need him to help us do that. If Daniel's saying no, he really can't be seen to be going back on that now. He's made a very strong statement. I wouldn't see Daniel backtracking on that at any price."
Though an appointment is expected with the next fortnight, Chelsea are still without a manager following the sacking of Carlo Ancelotti, and Redknapp feels it is "strange" that they are looking to make key signings at this stage.
Redknapp said: "It is very, very strange and difficult to understand, but this has been going on for quite a while, not just this week. It's been going on for the last three or four weeks, since Carlo Ancelotti lost his job. Somebody else at Chelsea is choosing the players - not the new manager."