Chelsea had an offer for Modric rejected out of hand by Spurs within two hours of it being received on Wednesday night, but the Blues are expected to return with an improved bid.
Redknapp, however, is determined to keep hold of the 25-year-old, who enjoyed a superb season at the heart of the Spurs midfield last year.
"Luka is not for sale,'' Redknapp said. "If there has been a bid of £22 million that is ridiculous. There are people being sold for £20 million who are not fit to lace Luka's boots.''
Chelsea owner Roman Abramovich is looking to rebuild the squad at Stamford Bridge while simultaneously reducing its average age, after a relatively disappointing campaign which saw the club lose out to Manchester United in both the Premier League and Champions League.
Modric fits the bill, but the former Dynamo Zagreb star's agent Nikky Vukan insisted on Thursday it would take substantially more than £22 million to prise the playmaker away from White Hart Lane.
However, Vukan, hinted that a deal could still on the cards if decent bid was received.
"Luka is happy at Spurs but if an offer came in that was acceptable to the club and player, we would be willing to discuss it," Vukan said. "In my opinion, £22 million is a valuation that is too low for the player.
"The price that has been written greatly undervalues the price that the club values him at the moment.
"If there has been a bid of £22 million I am not surprised that the club have rejected it. That figure is near to the fee that Spurs paid for Luka (£16 million).''
Modric has been heavily linked with a move away from Spurs after the club failed to secure qualification for the Champions League, and has hardly distanced himself from such speculation with some of his recent quotes.
"I'm a Tottenham player and will be in London on July 7 to begin preparing for the season," Modric has been quoted as saying. "But I want to say that transfers could occur later. In England it is often the case they happen on the last day of the transfer period, August 31.
"So it is pointless to worry about anything now. If my situation changes after the start of preparation it would not be a problem."
The Croatian playmaker joined Tottenham from Dynamo Zagreb in 2008 for a fee in the region of £16 million.