UFC flyweight Paddy Holohan, a 27-year-old Irishman who debuted with the organization in 2014, today announced his retirement from the sport.

In a lengthy social-media post, Holohan said a rare blood-clotting disorder, Factor XIII deficiency, has left him unable to pass his medical exams and get clearance for a license.

The disorder affects just one in 5 million people, and though it posed no danger to his opponents, he said, it’s still forcing a premature end to his nine-year pro career.

According to the National Hemophilia Foundation, Factor XIII (FXIII), or fibrin stabilizing factor, deficiency is the rarest factor deficiency, and “it is inherited in an autosomal recessive fashion, meaning that both parents must carry the gene to pass it on to their children; it affects men and women equally.” Additionally, it can lead to blood clots and spontaneous intracranial hemorrhaging, as well as “bruising, nose and mouth bleeds, muscle bleeds and delayed bleeding after surgery.”

Holohan (12-2-1 MMA, 3-2 UFC), an honorable mention in the USA TODAY Sports/MMAjunkie MMA flyweight rankings, was slated to Willie Gates (12-6 MMA, 1-2 UFC) next month at UFC Fight Night 87, but officials are searching for a replacement. The May 8 event takes place at Ahoy Rotterdam in Rotterdam, Netherlands, and airs on FOX Sports 1.

According to UFC.com, officials weren’t made aware of the condition until after Holohan’s latest fight and that the fan favorite then “was advised by medical professionals to retire with his long-term health and safety in mind.”

Here’s Holohan full statement (via Facebook):

I've known this announcement was coming for a week or more now and it has only felt worse the more I have thought about… Posted by Paddy Holohan on Monday, April 25, 2016

Holohan joined the UFC after an elimination-round loss on “The Ultimate Fighter 18.” He went 3-1 in his four UFC fights, and he earned a “Fight of the Night” bonus in the loss to Chris Kelades. Most recently, he headlined UFC Fight Night 76 in October. Holohan, who ultimately suffered a submission loss to Louis Smolka, got the top spot on the Dublin card after a planned bout between Dustin Poirier and Joseph Duffy was scrapped.

For more on UFC Fight Night 87, check out the UFC Rumors section of the site.