Federer took a break during Miami and then began training again before Monte Carlo, saying he will do some more off-court work in between tournaments—potentially even skipping another Masters event.

Federer returned mostly pain-free in Madrid after a seven-week break last spring, but had mixed results. "Just maybe feeling that training was lacking from the weeks I lost in April," he said.

Everyone finishes their career because of injuries that limit our training.” Both Federer and Nadal retired as they struggled with injuries during the final few years of their career as the ...