Atlanta Hawks forward John Collins has been suspended 25 games for violating the NBA's anti-drug policy, the league announced on Tuesday.
The league said he tested positive for Growth Hormone Releasing Peptide-2 (GHRP-2).
Collins told ESPN's Adrian Wojnarowski that he plans to appeal the suspension, which was set to begin on Tuesday night when the Hawks host the San Antonio Spurs.
"First I want to apologise to my team-mates, the Hawks organisation, our fans, partners and community as a whole for this situation," Collins said in a statement to Wojnarowski.
"I understand the impact this matter has on what we are trying to achieve together this season, and I am incredibly frustrated and disappointed in myself for putting all us in this position.
"I have always been incredibly careful about what I put in my body, but I took a supplement, which unbeknownst to me, had been contaminated with an illegal component. I plan to appeal my suspension in arbitration so I can get back on the court as soon as possible and continue to contribute to our 2019-20 campaign."
The 22-year-old is in his third NBA season and is part of a young nucleus for the improving Hawks, which includes second-year guards Trae Young and Kevin Huerter, as well as rookie Cam Reddish.
The Hawks made Collins, a Wake Forest product, the No 19 overall pick in the 2017 Draft.
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In 140 career games (90 starts), he is averaging 14.6 points and 8.4 rebounds per game. In five games this season, he is averaging 17.0 points and 8.8 rebounds per game and shooting 47.4 per cent from three-point range.
Phoenix Suns center Deandre Ayton also was suspended 25 games last month when he tested positive for a diuretic.