Three-time major champion Stan Wawrinka will not play in the ATP Masters events in Indian Wells and Miami as he continues to recover from knee surgery.
The 32-year-old Swiss retired from his Provence Open match against Belarus' Ilya Ivashka last week, only his fourth tournament since Wimbledon last year.
He missed the rest of the 2017 season after having surgery in August.
"I need to be patient and give my body the time it needs, but my goal is to come back on the clay," he said.
The clay-court season begins next month after Indian Wells and Miami, culminating with the French Open at Roland Garros - where Wawrinka won the title in 2015 and reached the final last year - between 27 May and 10 June.