The 23-year-old midfielder, who featured in Saturday's 5-0 win over Real Betis, has been handed a new long term deal by Rafael Benitez's side.
Casemiro has signed a six-year extension to his Real Madrid contract, the club confirmed on Monday.
The 23-year-old joined the Spanish side from Sao Paulo in 2013 and spent last term on loan at Porto where he became a key player for the Portuguese side.
The Br azil international featured for Rafael Benitez's side in Saturday's 5-0 win over Real Betis, coming on to play the final 25 minutes and helped set up Gareth Bale's second goal.
Casemiro's previous deal had been set to expire in summer 2017, but Madrid have now reaffirmed their faith in the midfielder by handing him a new contract which ties him to the club until June 2021.