At 5-1 in the third set, Holmgren felt so bad that he was forced to throw up on the side of the court.
Video from the ATP Challenger reveal that a person rushed in with a waste bin to help the struggling Holmgren.
The Danish tennis player was clearly uncomfortable, and in the end chose to withdraw against Colombian Nicolas Mejia when the scoreline was 7-6 (7-5), 5-7, 1-5 in Mejia's favor.
It was a close match in the first two sets before Holmgren got into trouble.
The early exit in Lexington comes after a string of good results over the summer. At the end of June, Holmgren qualified for the Grand Slam tournament at Wimbledon for the first time, where he even reached the third round.
He then won a Challenger tournament in Granby, Canada, before losing in the second round in Bloomfield, USA.
Holmgren has had 11 wins and only 1 defeat from 23 June to 23 July.
27-year-old Holmgren plays most of his matches on the ATP Challenger Tour, which is a level below the ATP Tour, where he has participated in individual tournaments.
In addition, he has tried several times to qualify for Grand Slam tournaments, in which he succeeded for the first time at Wimbledon.