The 28-year-old Swedish international lost consciousness in his home on Tuesday, 20 February 2024, and was transferred to Aarhus University Hospital, where he was admitted and put in a ventilator.
Tests showed he had suffered several blood clots because of a rare inflammation of the blood vessels in his brain putting his life in serious danger.
Olsson spent weeks in the hospital fighting for his life, but thanks to the timely medical intervention, the 29-year-old’s life was saved.
Referring to the first few weeks after his collapse, he said: "I was basically dying. I was not contactable and I have no memories from that time."
He added, "I've got through the worst part. I've had to think, be positive, and have patience with everything."
The Swede came through Arsenal's academy and made one appearance for the Gunners before he decided to join FC Midtjylland after a successful loan spell in 2015.
Olsson was also in the stands when FC Midtjylland won the Danish championship on 26 May 2024.
In March 2025, the midfielder canceled his contract with FC Midtjylland after slowly fighting his way back to the training pitch, with the prospect of returning home to Sweden.
He subsequently left FC Midtjylland to sign a new contract with his childhood club IK Sleipner, playing their trade in the third Swedish tier.
On Saturday, Kristoffer Olsson then completed his long battle to get back to action when he started in a training match against Österåker United, where he scored a great goal after 14 minutes of play.
Olsson, who has reached 43 caps for the Swedish national team, also played for Krasnodar and Anderlecht, besides playing 70 games for FC Midtjylland in the Danish Superliga.