Jannik Sinner wears glucose monitor in Monte Carlo training as team probes Roland Garros collapse

Return to the practice court

Three weeks after the second-round exit at Roland Garros that ended with a sudden physical collapse against Juan Manuel Cerundolo, Jannik Sinner is back hitting balls on the hard courts of Monte Carlo. A short video, recorded from a private balcony and captioned "someone watches Netflix, I watch Sinner training", shows the 24-year-old Italian without a shirt, executing forehand and backhand volleys. When he turns around, a small white patch is visible on the back of his left arm.

What the sensor actually measures

The device is a CGM (Continuous Glucose Monitoring) sensor, applied to the triceps. It does not sample blood but measures glucose in the interstitial fluid just beneath the skin via a filament that penetrates five or six millimetres. Readings are taken every few minutes and transmitted by Bluetooth to a receiver, building a real-time curve of glucose trends throughout the day, during sleep and during exercise. The sensor is sold in pharmacies without prescription and is not a marker of illness on its own.

“It is a device that continuously measures capillary glycemia. It is mainly used by type‑1 diabetic patients on insulin therapy, but it can be bought and applied by anyone who wants to observe how blood sugar varies during the day, including athletes.”

The medical puzzle after Paris

Sinner had dominated Cerundolo for two and a half sets on 28 May before his energy cratered. He subsequently underwent blood and cardiological tests, first at JMedical in Turin and then spending two days of day‑hospital exams at the San Raffaele hospital in Milan. The checks found no underlying pathology. Adding the CGM to his daily routine is a further precaution: his team wants to monitor how his glucose responds to prolonged effort, heat, nutrition and the timing of carbohydrate intake, especially with Wimbledon starting on 29 June and 2,000 ranking points to defend.

A shared tool on tour

The CGM is not new in elite tennis. Alexander Zverev wears one because he is diabetic. Novak Djokovic has used the device in the past, and Holger Rune was recently seen with one while recovering from a long injury layoff. Sinner joined Rune for a practice session in Monte Carlo in the same period, underlining how far the search for marginal gains has spread among the top players.