He wrote: "Well that was a wild New Year's Eve". Half the family hit with the Australian flu virus and some even left in hospital with it, ' he said in the post which has since been deleted.
The MMA fighter and boxer said that he had been left shaken by the illness, which has affected many people in Ireland this festive season.
'One of the most intense few days I've gone thru.
He thanked his family, friends and staff for supporting him and wished his fans a happy new year.
MailOnline has contacted Conor's representative for comment.
Despite the scary news, 29-year-old brawler Conor - who turned to boxing in 2017 to take on Floyd Mayweather in a Las Vegas bout - had some positive words in his Instagram post.
Step inside Conor McGregor's after fight party.
The MMA fighter memorably took on boxer Floyd Mayweather Jr in a hotly-anticipated face off at Las Vegas' T Mobile Arena on August 26 past year, which the Irishman lost.More news: Assam: ULFA (I) military leader's finds place in updated NRC draft
Fianna Fáil Spokesperson on Health Billy Kelleher issued a warning to Minister Simon Harris on the Fianna Fáil website, asking that the resources are in place to deal with a possible surge in the number of people being admitted to hospital following a spike in the number of "Aussie flu" cases.
Doctors in the United Kingdom have warned that it could be the worst outbreak of the bug in 50 years, as official figures revealed cases more than doubled in just one week.
Public Health England reported a 156 percent jump in cases of infection as figures revealed 1,111 people were struck down with it last week.
Experts have warned that an outbreak of Aussie Flu could be the worst type of virus to attack in over 50 years.
Some of Australia's A&E units had "standing-room only" after being swamped by more than 100,000 cases of the H3N2 strain.
Australia experienced the worst flu pandemic since 2009 during last year's winter season - typically between June and August - according to the country's department of health.
United Kingdom medical experts are braced for a deadly epidemic after observing Australia battle one of its worst-ever flu seasons.