Raonic's retirement in Tokyo calls season into question

Just days after expressing his concerns about the toll the tennis season takes on players' bodies, Milos Raonic retired from his second-round match in Tokyo versus Yuichi Sugita.

"I believe out of those of us that finished top five last year, I'm the only guy still trying to play this year, and none of the top five played the US Open," Raonic said after his opening-match win, before the retirement.

The other top-five players were Andy Murray, Novak Djokovic, Stan Wawrinka and Kei Nishikori.

One can only speculate as to whether the trend of stars taking extensive time off to recover was inspired by the success of Roger Federer, who called 2016 a year after Wimbledon.

Then there's Serena Williams, who truncated her 2015 and 2016 seasons after the US Open.

But not everyone is one of the greatest players of all time. Tennis's financial and rankings incentives encourage players (to put it nicely) to play packed schedules, which is why structural changes may be necessary, some argue.

"You see how many people are injured right now. Half the top 10's out, 80 percent of players have some sort of pain right now," said Japan's Taro Daniel. There needs to be a bit more space between the tournaments; there are players doing crazy stuff like playing in the U.S. one week, China the next week, and after Roland Garros playing 15 weeks in a row."