Chelsea reportedly promised Eden Hazard a future move to Real Madrid last year if he stayed with the Blues for the 2018-19 season.
Both the Blues and Los Blancos sit third in their respective leagues, but Zidane's return will reignite hope for Madrid that they can challenge for the league title and the Champions League next year.
According to The Sun, Hazard's representatives have demanded that Chelsea honour their agreement from last year that he could finally leave Stamford Bridge if he remained there for one more season.
The report adds that Madrid will make an official offer for the play, potentially paying up to £90m for the 28-year-old.
Hazard has impressed under Maurizio Sarri, scoring 16 goals and registering 15 assists this season.