Australian basketball star Josh Giddey is being investigated by the NBA following an allegation the Boomers ace had an improper relationship with an underaged girl.

The Oklahoma City Thunder guard was on Friday (Sat AEDT) peppered with questions about the social media storm.

NBA spokesman Mike Bass confirmed the league is “looking into” the serious claims that went viral about Giddey on Thursday and continue to trend globally across various platforms.

A picture circulating the internet and understood to have been posted by the girl, alongside a shirtless Giddey, featured the caption “just f....d josh giddey”.

Giddey has turned comments off on his Instagram account, which has 514,000 followers.

In a since-deleted post, an anonymous social media user said a girl who is seen with Giddey in videos and photographs was a high school junior at the time. The social media account has since been deactivated.

Giddey, 21, fronted the media at OKC’s practice session but declined to go into any detail about the situation.

“Yeah, I mean, I understand the question, obviously,” he said.

“But there’s no further comment right now.”

In another response, Giddey said he got the question but was in no position to answer.

“I completely understand you guys want to know about it. But just for right now, I don’t have anything to say,” he added.

Giddey’s Thunder coach Mark Daigneault was also asked about the situation: “Personal matter, and I have no comment on it - and that will be my answer on anything related.”

Drafted to the Thunder with pick six in the 2021 draft, Giddey’s promising career could be seriously impacted by the allegations.

He was the youngest NBA player to record a triple-double — at 19 years and 84 days — and the first player since Hall of Fame member Oscar Robertson in 1961 to record three consecutive triple-doubles as a rookie.

Giddey is averaging 12.3 points, 5.7 rebounds, and 4.5 assists for a young Oklahoma City team that is off to a flying 11-4 start.

The 2021 NBL rookie of the year is a key part of the Boomers’ hopes of improving on their historic bronze medal in Tokyo at next year’s Paris Olympics.

It remains unclear if Giddey will play in the Thunder’s home match against the Philadelphia 76ers on Sunday AEDT.