Simplify the following text for a Grade 10 native English-speaking person.
Original: Juan MartÃ n del Potro was the defending champion , but chose not to participate this year , after undergoing a wrist operation in May and only starting to practice again in August .
Simplified: Juan MartÃ n del Potro was the defending champion , but chose not to compete this year , after a wrist operation in May and only starting to practice again in August .