DELRAY BEACH, Feb. 23 (Xinhua) -- Defending champion Juan Martin del Potro has withdrawn from the Mexican Open because of discomfort in his troubled right knee, just days after being granted a wild card for the ATP 500 event.

The 30-year-old Argentine announced his decision to miss the tournament in the Pacific resort city of Acapulco after his defeat to American MacKenzie McDonald in the quarterfinals of the Delray Beach Open in Florida.

"I won't be going to Acapulco," the world No. 4 said. "It was always going to depend on how I felt here [at Delray Beach]. And as I progressed I've given myself fewer chances of going to Mexico. I have to listen to my body."

The Delray Beach Open was Del Potro's first event since he suffered a fractured knee cap at the Shanghai Masters last October.

The 2009 US Open champion has been beset by injuries in recent years and long periods on the sidelines saw his career ranking plummet to 1,045th place in 2016.

Last year he won two ATP titles and reached the final of the US Open, where he was beaten by Novak Djokovic.