Yves Bissouma faces possible punishment from Tottenham after the midfielder filmed himself inhaling nitrous oxide on social media.
Spurs have confirmed they have opened an investigation into the matter, with the 27-year-old since apologising for his 'severe lack of judgement'.
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The Mali international uploaded clips of himself using the Class C drug - known as 'hippy crack' - onto Snapchat last weekend.
Bissouma could be seen laughing between taking hits of the balloon in footage he shared to his fans.
The incident came just hours after Spurs' final pre-season clash, where they lost 3-2 to Bayern Munich in the Visit Malta Cup.
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And he now faces an anxious wait over whether he will be reprimanded by club chiefs.
Issuing a statement, he said: "I want to apologise for these videos. This was a severe lack of judgement
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"I understand how serious this is and the health risks involved.
"And I also take my responsibility as a footballer and role model very seriously."
Meanwhile a Tottenham spokesman added: "We are looking into the events.
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"This will be dealt with as an internal matter."
As part of the Government's anti-social behaviour action plan last November, nitrous oxide was made a Class C drug under the Misuse of Drugs act.
This means that possession of the so-called 'laughing gas' with the intent to get high illegal.
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Repeat offenders could face a two-year jail sentence, along with an unlimited fine.
Dangers of inhaling nitrous oxide can lead to nerve damage, depression, brain disorders and hallucinations as well as memory loss.
The incident is a major blow to Spurs ahead of their Premier League season opener away at Leicester next Monday night.
Bissouma has starred in pre-season for the north Londoners, where he scored a superb solo effort in the 2-0 win over QPR at Loftus Road.
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The ex-Brighton man rediscovered his form under Ange Postecoglou last season, where he proved to be a key player - making 28 top-flight appearances.
Bissouma may have already found himself in hot water with Spurs chiefs after he appeared to let slip that teammate Emerson Royal is on his way out.
The right-back is currently in Italy where he is set to join AC Milan on a permanent deal.
Again taking to Snapchat, Bissouma shared a video of himself in a Spurs training kit, where he and the defender shook hands before embracing in a hug.
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At the bottom of the video, he wrote: "One of the best guy (sic) I've ever seen in my life all the best there brother I love you I'll come see u soon there."