Jannik Sinner is out of the French Open in the biggest shock of the tournament so far after struggling with injury in a five-set loss to Juan Manuel Cerundolo in the second round in sweltering Paris conditions.

World number one Sinner was the heaviest favourite for the men's title since the great Rafael Nadal in 2009, with no-one coming close to challenging him on the clay in recent weeks.

Sinner was bidding to complete the career Grand Slam at Roland Garros, and few expected him to fall short - but just as Nadal suffered an early exit 17 years ago, the Italian will now have to wait for another chance at Paris glory.

Sinner was two sets and 5-1 up before a remarkable change of momentum when fitness issues plagued his game.

The 24-year-old appeared laboured on court with a dejected expression as he lost the next three games, including 11 straight points, before calling for the trainer.

Sinner could be heard saying he felt "dizzy" and like he "wanted to vomit" and took a mid-game medical timeout before returning to court.

After dropping the third set, Sinner failed to regain his fitness as Argentina's world number 56 won 3-6 2-6 7-5 6-1 6-1.

It is a bitterly disappointing way to exit the tournament for Sinner, whose favourite tag was enhanced further with defending champion and great rival Carlos Alcaraz missing with injury.

With 24-time Grand Slam-winner Novak Djokovic also nearing the end of his illustrious career, fitness was expected to be one of the biggest obstacles to Sinner's bid for glory.

Paris has seen unseasonably hot weather, with temperatures topping 34C, and Sinner has struggled previously in extreme heat.

Sinner was also on a 30-match winning streak, having won five Masters 1000 titles in a row over the past three months on hard and clay courts.

He cramped badly in temperatures close to 40C at this year's Australian Open, and admitted he "got lucky" when the heat rule was enforced in his third-round match against Eliot Spizzirri in Melbourne.

After opening his campaign against Clement Tabur in Tuesday's cooler night session, Sinner was first on court against Cerundolo in a rare move by Roland Garros organisers.

The last time a men's number one opened proceedings on Court Philippe Chatrier before the semi-final stage was 10 years ago, when Novak Djokovic beat Tomas Berdych in the quarter-finals.

Although Sinner seemed to benefit initially from the early start, the physical issues that have hampered his display in previous matches in extreme heat resurfaced.