Abdelhak Nouri, the Ajax midfielder who collapsed during a friendly on Saturday, has suffered "serious and permanent brain damage".
The Netherlands underage global was airlifted to hospital in Innsbruck, Austria after suffering a cardiac arrhythmia during Ajax's game against Werder Bremen.
In a second tweet Ajax said their "thoughts and prayers go out to him and his loved ones in this hard time".
Tests today have sadly revealed the extent of Nouri's brain damage, which according to a club statement is said to be "serious and permanent".
An initial brain scan at the start of the week couldn't find any anomalies, while his heart was "functioning normally".
It is expected Nouri will soon travel to Amsterdam for further treatment, but the chances of recovery are low.
The incident occurred after the 70th minute of the game, when he collapsed suffering from cardiac arrhythmia, which is an irregular heartbeat.
Ajax chief executive Edwin van der Sar, their former goalkeeper, told the club website: "This is the worst possible news".
Two days ago, the club said tests had shown that the Amsterdam-born player's heart was "functioning normal and appears to be undamaged", but tests could not at the time be conducted on his brain as he remained asleep. "Unfortunately we'll never know how far his star would have risen".
Nouri - a product of Ajax's youth system - made 12 senior first team appearances for the club last season in the Eredivisie and Europa League respectively, and has represented the Netherlands at youth level from U15 to U19.