Over the past few days, there has been a growing sense of anxiety surrounding the health of ATP World No. 1 Jannik Sinner. The Italian superstar reportedly traveled to Milan for a non-routine medical examination of his knee.According to Eurosport, Sinner is now "doubtful" for the ATP Masters 1000 event in mid-August. Meanwhile, others have a more optimistic view of Sinner's status, citing that they saw Sinner train in Monte-Carlo. 🇮🇹🤕 Jannik Sinner’s medical visit yesterday was, reportedly, NOT routine and focused on an ongoing slight knee issue🎾 He may undergo a second test soon, before leaving for Cincinnati - although just going straight into the US Open isn’t ruled out 🗣️ https://t.co/zWCu2iY09m pic.twitter.com/nZo2TibrZa— Olly Tennis 🎾 🇬🇧 (@Olly_Tennis_) August 6, 2026Luckily for Sinner, he still has time for evaluation and recovery, as he has taken a prolonged break after winning Wimbledon in early July.Sinner has already missed the first two tournaments of the North American hard court swing: the Mubadala DC Open and National Bank Open presented by Rogers. If he misses the Cincinnati Open, Sinner will have no warm-up before the U.S. Open.— jannik sinner files (@jannik_files) August 6, 2026Sinner is not the only superstar dealing with injury woes. Earlier this week, Carlos Alcaraz pulled out of the Cincinnati Open. Alcaraz has not played since April due to a right wrist injury, and will have to defend his U.S. Open title with no warm-up (assuming he is able to play by then).As for Sinner, this is not the first time this year the sports world has closely followed his doctor's visits. Sinner melted in the Parisian heat at Roland-Garros, suffering a second-round loss. After the early exit, Sinner returned home to Italy for extensive medical evaluations. He was given the all-clear to play and proceeded to win Wimbledon.There seems to be some discomfort in the knee, maybe new checks in Milano before leaving for the USA. Let’s wait and hope for the best. 🤞🦊Via @Corriere pic.twitter.com/q41hrEVJe8— Janniksin_Updates (@JannikSinner_Up) August 6, 2026The most likely scenario is that Sinner will proceed with an abundance of caution. Sinner has a massive lead over Alcaraz and Alexander Zverev in the ATP Rankings. Defending his runner-up status at the Cincinnati Open is important, but not as big as the U.S. Open and busy fall schedule.Currently, Sinner is the World No. 1 with a singles record of 44-3 with six titles. Last month, he won his fifth career Major by defeating Zverev in the Wimbledon Championship match. Despite any challenges, the 24-year-old seems to have a solid understanding of managing his body throughout the marathon ATP season.— Janniksin_Updates (@JannikSinner_Up) August 6, 2026The 2026 Cincinnati Open will be held from August 13–23, 2026, at the Lindner Family Tennis Center in Mason, Ohio. The winner gets $9,415,725 in prize money and 1,000 points in the ATP Rankings.Stay locked into Sports Illustrated's Serve On SI for all of your tennis news from the court and beyond.Add us as a preferred source on GoogleFollow