The 21-year-old has committed to 12 more months after impressing at the capital club and helping it on its way to the Champions League final.
Atletico Madrid has confirmed that Saul Niguez has agreed terms on a new contract at the Vicente Calderon until 2021.
Wednesday's announcement means Saul, who came through the ranks at Atletico, has extended his previous deal by a further 12 months.
Saul made his debut for the club in a Europa League clash with Besiktas in March 2012, before going on loan to Rayo Vallecano for the 2013-14 campaign.
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