Sydney police are investigating the circumstances surrounding Gray's death - revealed when friends discovered his body at his Elizabeth Bay home on Monday.
A post-mortem examination is expected to determine a cause of the 46-year-old's death, but some media outlets have reported a syringewas found in his apartment.
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"That would be very not like him," his mother Georgina Gray told Network Ten."That wasn't him at all. He wasn't doing any kind of scene like drugs or anything like that."
Friends forced their way into Gray's apartment after he failed to answer numerous phone calls and did not show up for appointments.
Football Hall of Fame
Although retired as a professional player, Gray maintained strong links to the soccer community, working as a coach and trainer of junior teams.
"Nobody had a bad word to say about him and he helped save the careers of lots of good players... Mark Schwarzer, Steve Corica and countless others," friend Bob Caitlin said.
Gray played 35 matches for the Socceroos over nine years, after beginning his career with the Manly Vale and Western Suburbs clubs.
In 2004, he was inducted into the Football Federation Australia (FFA) Hall of Fame - Award of Distinction.
Gray injured in Thai attack
An experienced defender and midfielder, he started a 12-year national representative career in 1981, and was chosen for the senior Australian side in their 1984 World Cup campaign.
While visiting Thailand three years ago, Gray suffered injuries during an assault from which he never fully recovered.
"The doctors said he probably wouldn't ever be 100 per cent, but he was progressing," Mr Caitlin said.
Details of Gray's funeral are yet to be released.
Meanwhile, police are appealing for public information about the death. Anyone who has information can call Crime Stoppers on 1800 333 000.
