Jannik Sinner arrived at the French Open last month with fans dreaming of him finally lifting the Coupe des Mousquetaires. Instead, his desire for the ultimate clay court glory ended in disappointment after a shock defeat to Juan Manuel Cerundolo following Carlos Alcaraz’s withdrawal from the tournament. Now, ahead of his Wimbledon title defense, fresh training images have sparked concern, leaving fans wondering if something is wrong with the Italian.

A recent image of the current world No. 1’s training in Monte Carlo quickly caught fans’ attention. Many noticed a small device attached to his left arm and began wondering what it was.

The device is not unusual or a cause for immediate alarm for the players. It is a Continuous Glucose Monitor (CGM) sensor, which is used to track glucose levels. Rather than measuring blood directly every moment, CGM monitors glucose in the interstitial fluid beneath the skin. It helps show how glucose levels change throughout the day in a human body.

The device can reveal spikes after meals, drops during physical exertion, and the body’s response to heat, stress, or poor recovery. That information can be valuable for athletes preparing at the highest level.

For tennis players living with diabetes like Alexander Zverev, CGM sensors are a well-established medical tool. In physically healthy athletes like Jannik Sinner, however, they are mainly used to identify patterns and optimize performance.

An athlete can use the data to check whether they begin training with enough available energy. It can also highlight the overall glucose drops during long sessions or show how certain foods affect energy levels.

During the Roland Garros in Paris, heat became an important talking point. Even so, the Italian himself made it clear that he did not want to blame everything on the temperature alone.

However, medical science offers several possible explanations for symptoms like sudden fatigue, dizziness, weakness, or poor concentration. Heatstroke, partial dehydration, inadequate carbohydrate replacement, or an unusual metabolic response can all produce similar effects in a human body.

And it was not the first time that Jannik Sinner experienced such issues on a tennis court. Fans saw similar situations during his match against America Eliot Spizzirri in the AO and against the Dutch Tallon Griekspoor in Shanghai last year, where he was also forced to retire.

Research on the device used on athletes suggests these sensors can help personalize nutrition plans. At the same time, medical experts caution that CGM readings should never be treated as absolute truth or a direct predictor of performance. The data it produces always requires medical, nutritional, and physiological context because every athlete responds differently.

Although the training image has now spread across the various social media platforms, there is no confirmed indication that Sinner is dealing with diabetes. Still, with The Championships fast approaching, many fans remain concerned and will be watching closely as his preparations continue.

Tennis fans show their concern over Jannik Sinner’s health ahead of Wimbledon

As soon as the director of Punto De Break, José Morón, shared the training image, tennis fans flooded social media with concern over Jannik Sinner’s condition. One fan wrote, “If it is what it seems… it’s a glucose sensor and it’s not for sports use, but for diabetes patients. No more stories,” while another netizen simply commented, “Diabetic sinner.🤨”.

Another fan brought Novak Djokovic into the discussion by adding, “He should go to an applied kinesiology doctor. Novak had similar situation at the beginning of his career. He would crash. They figured out that he had a mild case of reaction to gluten. Once he went gluten free it never happened anymore. People don’t realize that Novak crashed”. The comment referred to how, back in 2010, the Serbian GOAT dealt with mid-match collapses and fatigue before meeting Dr. Igor Cetojevic.

According to the tennis fan, muscle testing revealed severe food intolerances, especially to gluten. Removing those foods from Novak Djokovic’s diet back then completely changed the course of his career.

Meanwhile, another user wrote, “Please He needs every technology, every machine he can get to keep fit,  I don’t want him crashing out again like he did in RG”. One more fan argued that if the Italian cannot handle demanding five-set matches in Slams, it could become much harder for him if more players besides Carlos Alcaraz continue pushing him deep into Grand Slam battles, adding, “If his body doesn’t respond to 5-set matches… Enjoy it while only Alcaraz competes with him But if two others emerge at that level, goodbye to winning grand slams”.

Just a week ago Sinner has undergone several medical examinations at San Raffaele Hospital. Those included a stress electrocardiogram, a Holter monitor, and a cardiac MRI as part of his evaluations.

His recent physical struggles and withdrawals have also left former world No. 1 and 4-time Grand Slam winner Kim Clijsters puzzled.

And as the training image continues circulating online, speculation has only grown among tennis fans. For now, though, their biggest hope is simply to see a fully healthy Sinner ready to compete when SW19 begins later this month.