Williams pulled out of Madrid, a top-tier event for both the ATP and WTA, last Friday, citing the flu. On Monday, Federer also withdrew after an old back injury flared up during a Saturday practice session.
Federer and Williams, the twin pillars on which the game's current global popularity rests, are both 34 years old. With a quarter of the year elapsed, each of them has played just three events. While both have earned the right to be selective, neither has won any of those events.
Both players have repeatedly said they have no plans to retire any time soon. But the bodies of the players might be telling them otherwise.
In Williams' case, her heart also might be a dissenting voice, even though early this year her coach, Patrick Mouratoglou, told the French sports daily L'Equipe that she could play for "another five years."
Federer and Williams are almost as strangely similar as they are wildly different. Their base constituencies might differ, and even their shared crossover fans probably like them for very different reasons. But the parallels are as crystal clear and quantifiable, and as plainly visible, as the Matterhorn or Washington Monument.
Start with the shared age and then proceed to the record books, where, among other distinctions, Federer is the men's all-time Grand Slam singles titlist with 17, while Williams has 21, just one behind Steffi Graf's Open era women's record. There are shared personal preferences, like their affection for Wimbledon. (Federer has seven titles there; Williams, six.)
Last year ended with Williams being denied a historic calendar-year Grand Slam by just two wins. But despite the shortcoming at the US Open, she was seemingly poised to try again -- or short of that, at least primed to catch and perhaps surpass Graf in the singles title derby.
Federer? He was rejuvenated. Not exactly a successor to top-ranked Novak Djokovic (in tennis you don't "succeed" anybody at age 34), but the game's best candidate to curb the rampaging Serb's appetite.
But here we are. In Federer-Williams lockdown.
An area of concern: Say you're like them and you're lucky enough to forestall the inevitable. You continue to play great, long after you're expected to decline. Does that mean that when you finally do begin that downward slide, it's at an accelerated pace -- more luge run than sail into the sunset?
It's a scary idea. Scary for fans, for television networks and sponsors, for everyone in tennis. As much as Rafael Nadal, Djokovic, Victoria Azarenka and others bring to the game, Federer and Williams are a one-two punch the likes of which we haven't seen before.
Sure, we had Chris Evert and Jimmy Connors, and Andre Agassi and Graf. But Roger and Serena are even bigger, because their similarity is so different.
Federer had played his way back into shape following his knee surgery with three strong performances in Monte Carlo. He seemed ready to restart his year in Madrid. Opportunity gone.
He tried to sound optimistic as he told the press in Madrid, "It's the back stuff I kind of know [from my history]. I'm OK with it. At least I know what it is."
Williams' state is more opaque. Even when she was winning matches last year, often having to dig herself out of self-excavated holes, she clearly struggled with her emotions. She was stressed. She was fried. The quest for a Grand Slam left her nerves raw. It would be different in 2016 after a long rest.
It has not been very different. Williams continues to battle herself as well as her opponent. She often looks distracted. Lethargic. She seems to want to give something that isn't there. She seems to resent having to give it. Or can't find it to give. It's a vicious cycle. Maybe she will come out of it and relax.
Mouratoglou's five-year prediction could apply to Federer as well as Williams. But it ought to be considered in light of the full quote. Mouratoglou told L'Equipe: "[Williams'] calendar would need to be very carefully managed. If the desire is there, and there are no major injuries, she could keep going for another five years."
The first condition is being met by both players. The two hypotheticals in the quote are an entirely different story. Federer probably is worrying about just one of them, injury. Williams might be thinking about both.