Sweden midfielder Kristoffer Olsson has been placed on a ventilator in hospital after losing consciousness at home.
Midtjylland said the ex-Arsenal player, 28, is “suffering from what appears to be an acute brain-related illness”.
The Danish club announced he was taken to Aarhus University Hospital on 20 February.
Midtjylland said they felt “compelled” to release an update due to “increasing rumours and speculation about Kristoffer Olsson’s recent absence”.
“Everyone in FC Midtjylland is of course deeply affected by Kristoffer’s sudden illness,” the club said in a statement on Tuesday.
“Kristoffer Olsson is suffering from what appears to be an acute brain-related illness, which is neither due to self-inflicted harm of any kind nor due to external factors.
“A team of leading Danish medical experts are currently working under pressure to make a diagnosis and initiate the correct treatment.”
Olsson came through Arsenal’s youth academy and made one appearance for the Gunners before he joined Midtjylland permanently midway through the 2014-15 Premier League season.
Arsenal said on X, formerly known as Twitter: “Get well soon, Kristoffer. We wish you a full and speedy recovery.”
Olsson, who has made 47 senior appearances for Sweden, has had spells at Swedish side AIK, Krasnodar in Russia and Anderlecht in Belgium between two stints with Midtjylland.
“Keep fighting Koffe!” the Swedish football association said on X, formerly known as Twitter. “The entire Swedish football family are thinking of you and hope you soon recover. Our thoughts also go to Kristoffer’s loved ones at this difficult time.”
Olsson has missed Midtjylland’s two most recent Danish Superliga matches and last featured for the club against Fredrikstad in the Atlantic Cup on 9 February.
“Since being admitted, Kristoffer has been surrounded by his immediate family and FC Midtjylland staff members, as well as specialists in the field,” the club added.
“FC Midtjylland urges the public to show respect and understanding so Kristoffer, his family and doctors are allowed the peace of mind to ensure Kristoffer gets better and recovers as successfully as possible.”
