The 32-year-old Spaniard was contemplating cause and effect after painful knee tendinitis flared up during his quarter-final victory over Karen Khachanov at the ATP Indian Wells Masters on Friday.
The longtime foes have amassed 37 Grand Slam titles between them - Federer with 20 and Nadal with 17 - and built a unique relationship over 15 years and 38 prior matches, not to mention countless promotional and charitable activities off the court together. [Nadal] played so well this week and I thought he was playing some of his best tennis again.
"What I'm going to do is come back home and try to do a smooth transition to clay, try to be 100 percent for the first event, that's going to be Monte Carlo for me", he said.
It was just the fifth time in Nadal's career that he had conceded a walkover, and the first to Federer.More news: Europa League draw: Arsenal in nightmare quarter-final
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He appeared to be on the verge of tears on Saturday as he spoke to the media.
He admitted that he sometimes is sad because he feels at a disadvantage against his opponents due to his continued knee issues that force him to limit his practice and playing time. "With all this stuff, I still where I am today".
Nadal reached the final at the Australian Open, and while he lost in straight sets to Novak Djokovic he said it was a positive sign after he had to pull the plug early on his 2018 season. He's ranked No. 2 in the world and has a match record of 11-2.
"Still tough because I felt more or less OK during this beginning of the season in terms of my knee", Nadal said. "Of course my goal and my idea is to be ready for tomorrow", Nadal said.
It would have been the 39th career meeting between Nadal and Federer, who advances to Sunday's final in pursuit of a record sixth title at Indian Wells and the 101st in his career. We've had so many epic battles and I know now that every one we have could be our last. Comedian Jon Lovitz served as chair umpire.