Ajax captain Siem de Jong will miss approximately six weeks of action after being diagnosed with a collapsed lung.
Following persistent tightness and coughing on Monday, the 24-year-old underwent a scan which revealed that he may have been playing with the problem during Ajax's opening two matches of the season.
De Jong will now be absent for his team's Eredivisie clash with rivals Feyenoord on Sunday, and is also unlikely to be available the Dutch title holders' Champions League opener in September.
The Netherlands international midfielder scored 16 goals in 42 appearances for Ajax last season.
