Delray Beach: Defending champion Juan Martin del Potro has withdrawn from the Mexican Open because of discomfort in his troubled right knee, just days after being granted a wild card for the ATP 500 event.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 after his defeat to American MacKenzie McDonald in the quarterfinals of the Delray Beach Open in Florida, reports Xinhua news agency. "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."