The 34-year-old star will leave the Old Trafford club at the end of his current contract, after joining the Reds in January 2014 and playing 285 games for United.
The club said in a statement: "Thank you for dedicating eight years of your career to United, Juan. Everyone at the club wishes you all the best for the future."
The news was announced shortly after United confirmed the departures of Edinson Cavani, Paul Pogba and Jesse Lingard.
Pogba, 29, became the most expensive player in the world when he joined United in 2016.
But he's now leaving the club for the second time, with United wishing him well with the rest of his career.
The club said as part of a lengthy statement: "Everyone at the club would like to congratulate Paul on his successful career, and thank him for his contributions to Manchester United.
"We wish him all the best for the next steps on a remarkable journey."
Pogba and Lingard both played for the club's academy teams during their younger years.
And the 29-year-old midfielder sent a message to the United fans after his exit was confirmed.
Lingard said on Twitter: "Born and bred a red. Over the last few weeks, I've been emotional about leaving a club that is family. After 22 years I’ve had so many special memories and moments that I will cherish forever. ManUtd will always remain in my heart. A massive thank you. Lots of love Jlingz [heart emoji] (sic)"