El Pais says the former Real coach had an agreement with president Florentino Perez in January that Bale would be sold at the end of last season.
Florentino was committed to the agreement - until Bale came off the bench and struck a spectacular goal in their Champions League final win over Liverpool.
At that moment, Florentino turned to fellow directors to declare the Welshman "was better than Cristiano" because he made "the difference" in the big games. After such a moment, there was no chance of the president going through with plans to sell Bale for the €100m he had agreed with Zidane over the New Year.
Upon learning that Florentino had reneged on their 'pact' without consulting him, Zidane felt insulted and this contributed to his decision to resign just days after the final.