Casemiro shared his decision in a video posted on social media, confirming his exit from Manchester United, where he is completing his fourth season after joining from Real Madrid.
"Knowing when a chapter comes to an end. Knowing when to say goodbye, especially when you feel you’ll always be remembered and respected," Casemiro wrote in his post.
"Four more months to give everything for this badge and for our goal. My respect and affection for Manchester United and its wonderful fans will last forever. Forever a Red Devil."
During his time at Manchester United, Casemiro has played a total of 146 matches, scoring 21 goals and providing 12 assists.