Sports Illustrated said Del Potro lost due to "personal problem."
From Sports Illustrated
By Courtney Nguyen
Juan Martin del Potro’s camp confirmed to SI.com that Del Potro flew home to Argentina after his opening-round loss at the Sony Open to deal with “personal problems.” His people said the problems aren’t serious, but they did cause him to lose focus when he got to Miami. Hope everything is all right for him.