Sinner announced his withdrawal from the Games on his X account.
"I am saddened to inform you that unfortunately, I will not be able to participate in the Paris Olympic Games," Sinner wrote in a post on X.
"After a good week of clay training, I started to feel unwell. I spent a couple of days resting and during a visit the doctor found tonsillitis and strongly advised me against playing.
"Missing the Games is a huge disappointment as it was one of my main goals for this season. I couldn't wait to have the honour of representing my country in this very important event. Good luck to all the Italian athletes who I will support from home."
Sinner was also due to play in the men's doubles alongside Lorenzo Musetti.
Sinner's withdrawal means world number two and 24-time Grand Slam champion Novak Djokovic will be the top seed in the men's singles draw.
The Olympics draw will be made on Thursday.
Sinner is the latest of a number of tennis players to withdraw from the competition, with Olympic silver medallist Marketa Vondrousova and Poland's Hubert Hurkacz pulling out of the tournament on Monday.
Other notable absences from the tennis at the Games include world number three Aryna Sabalenka, Ons Jabeur, Emma Raducanu and Ben Shelton.
The tennis tournament at the Olympics will take place from July 27th to August 4th at Roland Garros.
