Sinner quits Paris Open exhausted by late nights
The night before, the Italian started his match against American Mackenzie McDonald after midnight and battled to a three-set victory in two hours 16 minutes.
Sinner was due on centre court on Thursday as the fourth match on the schedule to face Australian 13th seed Alex de Minaur.
Darren Cahill, who coaches Sinner, said on Instagram that he was happy with the victory but criticised "zero care for players welfare with Paris scheduling".
Casper Ruud, the eighth seed, who lost to Francisco Cerundulo on Wednesday, echoed the criticism on Thursday.
"Bravo atptour way to help one of the best players in the world recover and be as ready as possible when he finished his previous match at 2:37 am this morning 14.5 hours to recover.. what a joke," the Norwegian posted on X, formerly Twitter.
Sinner arrived in Paris from Vienna where he won the title on Sunday in a final against Daniil Medvedev that lasted more than three hours.
On Thursday in Paris, Grigor Dimitrov opened the action by racing into the quarter-finals with a straightforward 6-2, 6-2 victory over Alexander Bublik of Kazakhstan.
Dimitrov, the world number 17, showed little sign of any effects from his three-hour win against third seed Medvedev the previous afternoon as he dispatched Bublik in just over an hour.
The Bulgarian will face either Hubert Hurkacz, the world number 11 from Poland, or Argentinian Francisco Cerundolo in the last eight in the French capital.
Andrey Rublev also moved into the last eight, beating Botic van de Zandschulp of the Netherlands 6-3, 6-3.
The Russian has already qualified for the ATP Finals in Turin later this month.
In an all-Russian match Karen Khachanov, the 16th seed, beat Roman Safiullin, who had eliminated Carlos Alcaraz, 4-6, 6-4, 6-2.