It is understood that the 40-year-old had collapsed after complaining of chest pains. He was running errands with his wife at the time, after going for a jog.
He was buried on Saturday morning and leaves behind six children, the youngest was born just under a month ago.
Kadir won the Match Male Class 'E' title at the 5th World Championships in Kuala Lumpur in 1997. Two years later, he won the gold medal in the same class at the Southeast Asian (SEA) Games in Brunei.
Singapore Silat Federation (SSF) chief executive officer Sheik Alauddin told TODAY that he is still reeling from the news about his friend who worked as a national coach for a few years after retiring from the sport.
Friday night, aged 40.
"I received a call from a friend yesterday, and I was in disbelief when he told me the news," the 46-year-old former three-time world champion said, with a heavy sigh.
"And then, one by one, I kept getting calls and messages from friends with the same news. It is a very sad day for the Singapore silat family.
"This just shows that death can strike anyone at any time. Somehow, it seems that it doesn't matter how fit or healthy you are."
Former national fencer Nicholas Fang remembers Kadir as "a great sportsman" as well as "a really nice guy." They had travelled to a few editions of the SEA Games together as part of the Singapore contingent during the late 1990s.
"He was a very fierce competitor but off the mat, he was very warm, genuine and always smiling," said Fang who is now the president of Singapore Fencing and a Nominated Member of Parliament.
Sheik said he will meet up with the SSF Council to discuss what forms of support the national sports association can provide for Kadir's family.