Ajax manager Frank de Boer will have surgery after snapping his Achilles while taking part in training.
The 45-year-old was playing a game of foot volley - which involves kicking the ball over a small net - with his players when he suffered the injury.
It happened the day after Ajax moved top of the Dutch league with a 2-0 over title rivals PSV Eindhoven.
Club officials said the former Netherlands defender may have an operation on Tuesday.
Ajax have six league games remaining this season, with their next match on 3 April against PEC Zwolle.