Hazard, 28, sustained the injury following a rash tackle from Belgian teammate and Paris Saint-Germain’s defender Thomas Meunier, during last week’s Champions League clash.
He was initially only ruled out for 10 days, but fears have been mounting after he was spotted still going using crutches to walk.
Now Madrid have confirmed they have discovered a small fracture in Hazard’s ankle – which has almost certainly ruled him out of the showdown at the Nou Camp on December 18.
A statement from Madrid on Thursday said: “Following tests carried out on our player, Eden Hazard, by Real Madrid’s medical department, the development of the perimalleolar bruising in his right leg has seen him diagnosed with an incomplete external microfracture in the aforementioned area.
“His recovery will continue to be assessed.”
Both Madrid and Barcelona have recorded 31 points out of their opening 14 matches, with just one goal putting the Catalans in top spot of their rivals.
Meanwhile, Meunier has revealed he failed in an attempt to contact Hazard and apologise following the 2-2 draw.
He told French outlet La Derniere Heure: “I am honestly sad. I tried to contact him directly after the match, but I couldn’t reach him.
“Aside from that, I saw two or three of his team-mates who said that he had taken quite a hit. I cross my fingers that it is not too bad.
“If there is one player who I really don’t want to injure, it’s Eden.”
Since joining Madrid in the summer, Hazard has struggled with his fitness and has only bagged one goal and provided four assists out of his 13 appearances.
Madrid have Espanyol and a trip to Valencia to come before El Clasico, with a home game against Athletic Bilbao on December 22 their final one before the winter break.
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