Roger Federer waving off the French Open to better prepare for the grass and hard-court seasons. (Kenzo Tribouillard/AFP/Getty Images)

LeBron James skipping the NBA Finals because he didn’t like the visitor’s hardwood? Bryce Harper bypassing the playoffs due to the opposing team’s unfavorable field? Unthinkable.

But that’s more or less what Roger Federer did when he decided to sit out the French Open — and the entire clay-court season.

The second Grand Slam on the tennis calendar is nearing its halfway point absent several of the game’s top stars. None are more prominent than the 35-year-old Swiss, who chose to forgo the red dirt of Paris to protect his surgically repaired knee and prepare for grass at Wimbledon, which he has captured seven times. Federer won at Roland Garros once, in 2009.

In addition to sparking curiosity, Federer’s decision to skip a Grand Slam event points to a shift in the sport where the physical demands are greater, the risk of injury more pronounced and the careers stretch longer.

“Spacing out how long, how many tournaments I have played, I believe that’s helped me,” said Venus Williams, 36, who is making her record 20th appearance at Roland Garros. (Etienne Laurent/EPA)

Nowhere was this strategy more evident than at January’s Australian Open. The final weekend was dominated by a quartet coming off long layoffs.

Federer hadn’t competed since Wimbledon in July, a strategy to shore up his left knee, before winning the title in Melbourne. Runner-up Rafael Nadal ended his 2016 in October to rest his injured left wrist, which caused him to pull out of last year’s French Open.

Serena Williams, who beat older sister Venus for her Open-era record 23rd major in Melbourne, didn’t play a match after losing in the U.S. Open semifinals in September. Venus played three events and six matches between New York and mid-October.

“They are protecting their greatest assets — their bodies,” said Darren Cahill, the former pro and ESPN commentator who coaches Simona Halep of Romania, the French Open’s No. 3 seed.

With pros competing well into their 30s and some seasoned stars taking more conscious breaks in midseason, their example could trickle down, even if Federer remains an exception for now.

The concept of balancing match play with calculated blocks of time to rest, practice and build up bodies — known as periodization — has been gaining traction the last decade, according to Todd Ellenbecker, vice president of medical services for the ATP Tour.

Ellenbecker said in an email that proper periodization “appears to allow players to play at optimal levels for longer periods and enjoy great success.”

Federer, an 18-time major champion, has been a master at scheduling breaks, one reason for his sustained success and durability, including his unprecedented run of 65 consecutive Grand Slam appearances. That ended in Paris last year.

“Look, the thing is, I had to take that time off,” Federer said in March of his long break in 2016. “It was not like I took off six months because I felt like that was the thing to do for the Australian Open.”

Federer, who went on to win back-to-back hard-court titles this spring at Indian Wells, Calif., and Miami, added: “But if you look at the big picture, sometimes you have to step away to come back strong. I always did that throughout my career. Maybe not six months, but I did it probably two to three times a year where I kind of stepped away and came back. It’s served me well. That’s why I think I’m still here today and actually eager and excited to play tennis still.”

The Williams sisters likewise have logged lighter tournament schedules than most of their peers throughout their careers. They have rarely played grass-court tuneups leading up to Wimbledon, where they have won a combined 12 singles titles.

“Definitely, I think spacing out how long, how many tournaments I have played, I believe that’s helped me,” Venus Williams, the 10th seed at Roland Garros, said Sunday. The 36-year-old American defeated Elise Mertens, 6-3, 6-1, on Friday to advance to the fourth round in her record 20th appearance at the French Open. (Serena, who is pregnant, is sitting out the remainder of the season.)

Players in previous eras were more apt to skip majors to improve their fortunes on clay or grass. Jimmy Connors and John McEnroe took a pass on the French Open to focus on Wimbledon a combined 11 times. Spaniards Carlos Moya and Albert Costa, both French Open champions, sidestepped Wimbledon a total of 12 times during their careers after competing in Paris.

Passing over one of the biggest tournaments of the year is not a strategy for everyone. For one, the current ranking system penalizes players for skipping certain events and is structured to incentivize participation on all surfaces.

Rising Austrian player Dominic Thiem, 23, who won his third-round match at the French Open, 6-1, 7-6 (7-4), 6-3, over No. 25 Steve Johnson on Friday, said he had no plans to curtail his schedule while he is “young” and “fresh” despite playing 27 events in 2016, more than any player in the top 10.

“Right now, I’m not going to skip a major,” the No. 6 seed said Sunday.

Even nine-time French Open winner Nadal, the No. 4 seed who rolled into the fourth round at Roland Garros with a 6-0, 6-1, 6-0 defeat of Nikoloz Basilashvili on Friday, was skeptical of taking too much time off.

“In my opinion, is important to have matches to have success,” Nadal said.

Skipping a Grand Slam is costly, too. With no guaranteed contracts as in team sports, less successful tennis pros need to play to earn a living. This year’s first-round losers in the French Open pocketed 35,000 euros, or about $39,000.

Former Davis Cup captain Patrick McEnroe said younger players generally need to cut their teeth and gain experience as they make their way up the rankings.

“But for players that are at that level and have played a ton of big matches, having that time when they don’t need to compete means they can train harder and smarter,” he said.

Highly decorated and financially set stars such as Federer have the luxury to take time off if they feel they need it. They also have the benefit of the “Federer rule,” which allows players over 30 with enough tour experience to skip a mandatory event without penalty.

Jay Berger, the U.S. Tennis Association’s head of player development for men’s tennis, said up-and-coming pros tend to chase ranking points and play too many weeks in a row, often on different surfaces. But he is seeing a trickle-down effect from the example set by established stars.

“I think they’re getting it,” he said. “And I think they’re learning from the older players as well.”

The benefit of the sport’s biggest draws extending their careers is obvious. A trend where they suit up less often could also be a double-edged sword. Many regular tour events struggle to stay in the black. Less star availability would make financial stability more challenging.

Chris Evert applauded Federer’s thinking.

The American, who won seven French Opens, more than any other woman, recalled skipping Paris to compete at Wimbledon during her final season in 1989.

“I didn’t want to stay out there for three hours and run balls down,” she said of the slower clay surface. “I wanted to shorten rallies — just like Federer.”