Jannik Sinner says he "could not find any energy" as he lost in the second round to Juan Manuel Cerundolo in one of the biggest French Open shocks in recent years - but the world number one did not believe the Paris heat was not to blame.

Italy's Sinner was the heavy favourite for the title, having dominated the men's tour in recent months, and was on a 30-match winning streak going into Thursday's match.

After dropping just eight games in his Roland Garros opener against Clement Tabur, Sinner was in similarly commanding form against Cerundolo, leading 6-3 6-2 5-1 before suffering a dramatic physical downturn.

The Italian laboured around the court and lost three successive games before calling for the trainer, saying he felt "dizzy" and "wanted to vomit".

He took a mid-game medical timeout and left the court at the end of the third and fourth sets, but could not regain his fitness as he fell to world number 56 Cerundolo.

Although several players have attributed their on-court struggles to the unseasonably hot conditions in Paris, with temperatures peaking around 34C, Sinner downplayed the impact.

"I had no energy today. That can happen. Nobody is a robot," Sinner said.

"I woke up this morning, didn't feel very well and tried to keep points very short.

"In the beginning I was hitting very clean, very good, and then I just hit a wall.

"I started feeling dizzy. Very low on energy. I tried to serve it out but I didn't have a lot of energy."

Although he has previously struggled in extreme heat, most notably in his third-round win over Eliot Spizzirri at this year's Australian Open, Sinner said this was "a completely different scenario".

"It was warm, but not crazy warm. I feel like it was quite OK to play," the 24-year-old said.

"It was nothing against the heat, nothing against the weather. It was just me today, but it happens."

This is the first time since the 2023 French Open that Sinner has failed to reach the second week of a Grand Slam, and only the third time in that period that he has not reached at least the semi-finals.

He had won his only previous meeting with Cerundolo - a straight-set victory at Wimbledon in 2023 - and the Argentine had previously never beaten a player inside the top 10.

In terms of shock factor, it is reminiscent of Rafael Nadal's fourth-round exit at the hands of Robin Soderling in 2009 – his first defeat at Roland Garros in his fifth appearance.

Like Sinner, Nadal had a jam-packed schedule in the build-up to that year's French Open, winning titles in Monte-Carlo, Barcelona, and Rome and reaching the final in Madrid, where he lost to Roger Federer.

Ironically, Sinner was the heaviest favourite with the bookmakers for the Roland Garros title since Nadal 17 years ago.

But while this result is unexpected - and a huge opportunity missed for Sinner to complete the career Grand Slam - perhaps of greater concern for the Italian is his consistency over five sets.

Although hampered by illness on this occasion, the decline in his performance was stark.

Resorting to hit his way out of trouble as he struggled to move, Sinner committed 43 of his 64 unforced errors in the final three sets. His first-serve percentage plummeted to 47% in the fourth set and he won just 18 points in sets four and five.

This was also his 12th defeat in 18 matches when taken to a decider, and a third in the past 12 months after last year's French Open final against Alcaraz – where he let slip three championship points – and a semi-final defeat to Djokovic in Australia in January.

While this match came in at three hours and 36 minutes, he has also never won a match over four hours in seven attempts.

Sinner arrived in Paris in untouchable form, unbeaten on the clay and having won the past five ATP Masters 1000 events.

He had won 17 matches between 7 April and 17 May to claim clay court titles in Monte-Carlo, Madrid and Rome, dropping just three sets along the way.

He also became only the second man after Djokovic to complete the career 'Golden Masters' of winning all nine titles at least once.

However, Sinner had been on court for under two hours against Cerundolo when he suddenly showed signs of physical fatigue, clutching the top and back of his thigh midway through the third set.

Even after receiving treatment, he continued to move gingerly around the court, struggling to chase down shots and leaning heavily on his racquet between points.

Following the defeat, his packed schedule, which also included lengthy runs to back-to-back hard-court crowns in Indian Wells and Miami in March, was called into question.

Former British number one Tim Henman suggested on TNT Sports that Sinner should have skipped either Madrid or Rome.

"If I don't play Madrid or Rome, maybe I come here and I still have a day like this where you feel sick. Looking back it's always tough," Sinner added.

"I won three tournaments on clay. Incredible results. Amazing streak I've had.

"In the beginning of the year, this is my main goal here. A very early exit is not what I was looking for, but you also don't know if things would have changed if I would maybe skip Madrid and play only Rome."

Sinner suggested he will not play again before he begins his Wimbledon title defence on 28 June as he "recovers completely and mentally".