The son of the late national footballer Serbegeth Singh is upset with social media users blaming his death on a Covid-19 booster shot, saying that the post-mortem indicates it was a heart attack due to existing blockage.

"The doctors told us the cause of his death was 99 percent related to a heart attack as his post mortem showed three of his coronary arteries having blockages.

"All his vital organs were in perfect working condition, and there were also no signs of any allergic reaction," Sonuljit Singh told news portal Free Malaysia Today.

He said that social media users were being irresponsible and hit out at a viral message that links Serbegeth's death to a booster shot taken a few days before his death.

He said doctors informed him that his father also had cardiac fibrosis and likely had a silent heart attack in the past, considering the severe blockages in his arteries.

Sonuljit said that his father, siblings, and many relatives had a history of similar heart-related ailments.

"His heart was ready to go at any time, and it had nothing to do with the booster shot," he said.

Serbegeth, known as Shebby, collapsed while cycling in Kledang, Johor, on Jan 12.

During his youth, Singh wore the national jersey between 1982 to 1991 and played for the Johor, Kuala Lumpur, Negeri Sembilan, Pahang, and Perak teams before retiring in 1996.

He enjoyed his greatest success with Kuala Lumpur and won all major domestic honours in the game as well as the 1989 Sea Games gold with the national team.

After retiring, he was often a host or guest on sports programmes and had a stint as global advisor of the English club Blackburn Rovers in 2012.