World footballers’ union FIFPro has called for an urgent inquiry into medical treatment given to players at several top-tier clubs in Cyprus.

The demand follows reports in the Cypriot media at least four clubs have been giving injections of unidentified substances to players, and three players have been forced to quit the game with serious heart problems.

In a statement, the union said: “Because of concerns there is a link between the unidentified substances and the serious heart condition of the three players, FIFPro is calling for football authorities to help identify what was administered to them and to establish if their teammates are in danger.”

FIFPro said it has written to the Cyprus Football Association, the Cyprus Sports Organisation and European football’s governing body UEFA to express its concern and ask for immediate assistance.

The union, which represents more than 60,000 players worldwide, added it believes the substances have been administered by club doctors to aid recovery and it has been going on since the start of last season.