The clause is set at 500 million Euro, and is rumoured to be in place specifically to ward off the interest of Barcelona, who have become enamoured with Ceballos following his exploits at the European U21 championships.
Nonetheless, it is likely that the 26-year-old will remain in Manchester, especially considering the difficulty the clubs faced in agreeing on a deal for Alvaro Morata and the faith Zidane has shown to the Costa Rican.
Real signed highly-rated 19-year-old French defender Theo Hernandez on Monday, also for the next six seasons, for a reported fee of 30 million euros.
Real Madrid new boy Dani Ceballos insists he will do all he can to make the club's illustrious history even greater.
"You cannot imagine the pride and responsibility I feel at having joined Real Madrid", he stated on social media.
'I come with great motivation and with the two things that have brought me here: humility and hard work.
With the likes of Luka Modric, Mateo Kovacic, Toni Kroos at the Frenchman's disposal, Ceballos, who won 79 take-ons - the third highest total across the entire division - will give Madrid even more depth in central midfield.
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