Warning: The video above contains footage some may find disturbing.

A Croatian footballer who died on the pitch on Sunday, moments after the ball hit him on the chest, had suffered a heart attack, media reported on Monday. 

25-year-old Bruno Boban was playing for Marsonia in their Croatian Third Football League match against Slavonija Pozega when he was hit by the ball in the passage of play.

After jogging on for a few seconds, he crouched over to his knees and then collapsed face-down, seemingly losing consciousness. 

Medics spent 40 minutes trying to revive him as players and match officials looked on in despair, but it was to no avail. He was pronounced dead on the pitch. 

An autopsy on Monday showed that  Boban died of a heart attack.

At the time of his death, Boban was the top scorer in the third division's section east with 12 goals and Marsonija were fifth in the standings with 30 points from 17 games.

Boban had played for Slavonija from 2014 to 2016 before joining his brother Gabrijel at then top-tier side NK Zagreb. He moved to Marsonija earlier this year.

Several high-profile Croatian internationals extended their condolences to the Boban family on social media, with striker Mario Mandzukic saying: "Rest in peace Bruno and my deepest condolences to the Boban family as well as to all his friends and team-mates."

It was the first high-profile soccer death in Croatia since Zadar forward Hrvoje Custic struck a concrete wall with his head during a first division match with Cibalija Vinkovci in April 2008. The 24-year old died of brain injuries five days later