Modric has been the subject of intense transfer speculation this summer, with Chelsea having a bid for the 25-year-old rejected by Spurs, and Manchester United also said to be keen on the playmaker.
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The Croatian has gone public with his wish to leave White Hart Lane, but club chairman Daniel Levy has insisted the 25-year-old will not be sold.
But despite the uncertainty over his future, the former Dinamo Zagreb man's attitude and application in recent weeks has impressed his manager.
"His attitude has been first class. He has got on with it," Redknapp told Sky Sports.
"There would be players when they have wanted to move that really wouldn't have wanted to be playing today and not giving 100 percent.
"But he only knows one way to play. He is a fantastic boy and a great professional."
The Spurs boss also backed his chairman's stance over the future of the player, insisting the North London side couldn't afford to lose one of their star men.
"We can't just be selling our best players off," Redknapp added.
"Certain players just have that extra bit of class, like Rafa [van der Vaart] and Luka. We have some special players and we have to keep special players.
"They make the difference, so we have to keep Luka."
Modric captained Spurs as they marched to a 3-0 victory over Orlando Pirates on Saturday in the final of the Vodacom Challenge.
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