Humbert announced the conclusion of his season in October, with the Frenchman having suffered five consecutive defeats.

This included his withdrawal from the French team for the Davis Cup.

Humbert suggested he may have been impacted by an adverse reaction to being vaccinated against COVID-19.

Four of the five defeats came after he was vaccinated in Toronto.

"It’s very difficult to say, I’m absolutely not a doctor," Humbert said, according to Tennis 365.

"I did all the possible tests, and we found nothing, it was crazy.

"The doctors said there might be a connection with the vaccine, but it was useless to keep searching, because we don’t exactly know enough about the vaccine yet.

"But then 10 days after my shot in Toronto, of course I had played a lot, but after 45 minutes or one hour, I had cramps everywhere, and at the end of the season it was very tough for me to practice.

"After an hour I was exhausted."

Humbert tested positive for COVID-19 at the Australian Open earlier this year.

The Frenchman was informed of his positive test after his first-round loss to compatriot Richard Gasquet.

Humbert’s positive test was reportedly discovered as the Frenchman was about to leave Australia after his elimination from the tournament, leading to him being quarantined.

Humbert, the world number 48, suggested he had an adverse reaction to COVID-19 in Australia claiming he had not fully recuperated.

The 23-year-old said he was not the only athlete to suggest a reaction to COVID-19 vaccines.

COVID-19 vaccinations have been a major talking point in tennis this year, with men’s world number one Novak Djokovic of Serbia being deported from Australia on the eve of the tournament due to being unvaccinated.

The Serbian star was also forced to miss the Miami Open and Indian Wells Masters due to vaccine requirements.

Djokovic has played just four matches this year as a result.