That’s the warning from former Los Blancos chief Ramon Calderon, who was involved in the deal to take ex-Blue Arjen Robben to the Spanish capital in 2007.
Hazard confirmed on Wednesday, after Chelsea had won the Europa League, that it was “probably goodbye”.
He is expected to join Real Madrid having regularly confirmed his desire to play for the La Liga giants.
But Calderon has warned Real that they could face issues when it comes to negotiating a fee for the Belgian.
Calderon told Sky Sports News: “It seems Hazard is coming and that is really good news for Real Madrid.
“I think now it is a matter of money. The player has said clearly that he wants to leave and he wants a new challenge.
“It is not fair to keep a player who has been there for seven years and who has one year left on his contract.
“Of course Chelsea are not easy negotiators.
“I know that quite well because in 2007 I had a long negotiation with Peter Kenyon at the time and Roman Abramovich about Arjen Robben.
“He was not playing for Chelsea but despite that they said the price was £35m. At that time it was a lot of money.
“I tried to reduce it many times and we waited until the last minute but finally we paid it.”
Hazard had spoken about his future after Chelsea beat Arsenal 4-1 to win the Europa League.
He explained: “We will decide in a few days and the only target in my mind was to win this final.
“I have made my decision already and now I’m waiting on both clubs.
“I think it is a goodbye, but in football you never know.
“My dream was to play in the Premier League and I have done that for one of the biggest clubs so maybe now it is the time for a new challenge.”