"On Tuesday morning we received the terrible news that Olsson has been diagnosed with a sudden illness and is now in hospital on a ventilator," the national association Svensk Fotboll announced.

"The entire Swedish football family is with you in our thoughts and hope that you will recover soon."

Olsson's Danish club FC Midtjylland informed the public about the illness on Tuesday. According to the report, the 28-year-old lost consciousness in his home on February 20th and was subsequently admitted to the University Hospital in Aarhus. 

The central midfielder has been hospitalised there ever since and a team of specialists is working "intensively" on an exact diagnosis. The club will not release any further information until then.

Olsson played his last competitive match in the Danish league before the winter break on December 4th and was already missing from the squad for the start of the second half of the season on February 18th. 

He was a regular for the Swedish national team at the 2021 European Championships, among other things, but most recently played as a substitute.