World No. 1 Jannik Sinner and 24-time Grand Slam champion Novak Djokovic have both withdrawn from the Canadian Open for the second year in a row, once again depriving one of the ATP’s most prestigious tournaments of two superstars.Sinner, who earlier this month defeated Alexander Zverev in the Wimbledon final for his sixth major championship, cited health reasons for skipping the tournament, which begins August 2 in Montréal.“It is never easy to miss such an important event, but we believe this is the right decision to prioritize my health. I’m disappointed not to be there, but I look forward to returning to Montréal in the future,” he said in a statement.Djokovic’s absence is no surprise. The 39-year-old generally saves his body for the Grand Slams these days, and has played just two non-Grand Slam tournaments this year — Indian Wells and the Italian Open. Those events and the Canadian Open are three of the nine Masters 1000 tournaments on the tennis calendar, which are played at the level just below a Grand Slam.But for Sinner and Djokovic, missing that level of competition is not a problem. If they want a high-stakes tune-up ahead of the U.S. Open, there’s always Cincinnati, another North American Masters 1000 played on hard courts that begins in mid-August.Therein lies at least part of the issue the Canadian Open is facing. The event’s spot on the tennis calendar — just a few weeks after Wimbledon, but before another tournament of the same stature played on the same surface — combined with the expanded, 12-day format of Masters 1000 tournaments have made it vulnerable to withdrawals in recent years.Last year’s tournament was held even closer to Wimbledon, just two weeks after the grass-court major compared to three weeks this year, and was missing world No. 1 Aryna Sabalenka and four of the ATP’s top 10 players.What's the longest rally in tennis history?Tifo SportsThe 12-day Masters 1000 tournaments are nearly universally unpopular among players because of how they jam-pack an already overstuffed tennis calendar that runs from January until the end of November.But Sinner’s desire for an extended break is particularly unsurprising. The 24-year-old did not lose a match between March 6 and May 27 this year, in that time winning five Masters 1000 tournaments to become the youngest player to win all nine ATP events held at that level over the course of his career. The only other player to have completed the set is Djokovic, who did so at 31.