Chelsea are believed to have increased their offer for Luka Modric from £22 million to £27 million in the light of the player's desire to quit Tottenham Hotspur.
The Croatia international's head has been turned by a £22 million bid from Chelsea, who are in need of midfield reinforcement following the serious injury sustained by Michael Essien last week.
Modric launched a stinging attack on Spurs chairman Daniel Levy at the weekend after being told that he would not be allowed to leave White Hart Lane this summer.
Spurs boss Harry Redknapp admits the Luka Modric saga has become "very difficult" - but insists the midfielder is still not for sale.
But despite a fresh approach from the Blues, Redknapp claims Spurs are yet to receive another bid.
"If they are going to make an improved offer, I would think they need to," Redknapp told Sky Sports News. "Twenty-two million pounds for Luka Modric would be a joke if he was for sale.
"He is the most fantastic footballer, so the offer is a joke in terms of how much money they have offered and, most importantly of all, obviously we need to keep him.
"At the end of the day, it is up to the chairman. The chairman makes those decisions. I certainly wouldn't want to lose him, but it is a difficult situation.
"He is a fantastic boy, as I have said before, he is a great player. It is not easy when people come along and start offering you double, treble your wages. It must make it very difficult for him."