Stan Wawrinka has pulled out of the Masters events in Indian Wells and Miami as he continues to work his way back to full fitness following knee surgery.
The 12th-ranked Swiss went under the knife after a shock first-round exit at Wimbledon last summer and did not play another match until the Australian Open in January.
He only committed to playing in Melbourne on the eve of the tournament and suffered a second-round loss to Tennys Sandgren. Wawrinka has played three further events, in Sofia, Rotterdam and Marseille, but won only two matches and retired during his opener against Ilya Ivashka in France last week.
The 32-year-old, who has suffered defeats to lowly-ranked Mirza Basic and Tallon Griekspoor, has now decided to step away from the tour again and hopes to be fully fit for the clay season.
He said: "Unfortunately I need to announce that I won't be able to play in Indian Wells and Miami. They are both amazing events but coming back from a big surgery is complicated and, after having played a few tournaments, I have discussed with my team that it is best for me to build on the progress and go back to practice.
"I've enjoyed being back on tour playing matches and this gives me even more motivation to go back on the practice court. My goal is to find my highest level again and in order to do that I will keep working hard every single day."
Wawrinka is one of the strongest players on clay and reached the final of the French Open last year after winning the title in 2015.
He said: "I need to be patient and give my body the time it needs, but as of now my goal is to come back on clay. I love that part of the season and hope to be ready by then."
Andy Murray is already certain to miss both Indian Wells and Miami as he continues his recovery from hip surgery while the same could be true for Novak Djokovic, who recently had a small procedure on his troublesome elbow.
Rafael Nadal, meanwhile, was forced to pull out of this week's tournament in Acapulco, with the hip muscle problem he suffered in Australia still bothering him, and could yet miss more events. The BNP Paribas Open in Indian Wells begins on March 8.