Raheem Sterling will have to explain himself to Liverpool after apparently being filmed inhaling the legal high nitrous oxide.
Manager Brendan Rodgers said he regarded the 20-year-old as "super-professional" but would need to speak to the England international about his lifestyle.
Footage of Sterling appearing to take 'laughing gas' and pass out unconscious emerged online during the Reds' 2-0 Premier League win over 10-man Newcastle at Anfield on Monday.
Sterling impressed on the field, scoring a superb opening goal inside nine minutes, although he later missed two clear-cut chances, and afterwards off-field issues dominated.
Rodgers said: "For me it is something that when you are a professional sportsperson at the top level of the game, I don't think it is something you should be doing. It is as simple as that.
"But I will speak to him on it, to see what he says. We want players here who are super-professional and focused on their football. I know he is, he very much is focused on his football and improving as a player.
"As I have said before, young players make mistakes. As long as they learn from them, that is what is important."
The matter adds to the controversy and negativity currently surrounding Sterling amid a wrangle over a new contract. Sterling risked the wrath of supporters a fortnight ago by admitting he had rejected a £100,000-per-week deal in an interview that was not sanctioned by the club.
Another newspaper also published pictures of him allegedly smoking a shisha pipe over the weekend.
Rodgers, who stressed that any repercussions would be dealt with internally, did not feel the matter would be a distraction.
He said: "You see the way he plays. He is a kid that is very strong-willed and strong-minded. He should have had a hat-trick, his performance was outstanding."
Rodgers' sentiments were echoed by Sterling's former Liverpool team-mate, now TV pundit, Jamie Carragher.
Carragher told Sky Sports: "It's just important he learns from it because Raheem Sterling, for how good a footballer he is, needs to be on the back pages, not on the front pages and that's a problem for him in these last few months.
"But he's a young player, he made a few mistakes and hopefully in years to come he learns from them."
What is Nitrous oxide?
Nitrous oxide is a gas that can make people feel relaxed, euphoric and giggly, leading to its nickname "laughing gas".
It is not illegal to be in possession of the substance, sometimes also known as "hippie crack", although it is prohibited from being sold in England and Wales to under-18s if there is a risk they will inhale it.
According to the government-funded drugs helpline FRANK, there is a risk of unconsciousness or even death from lack of oxygen - the nitrous oxide effectively pushes the oxygen out of the body.
The risk is increased if the gas is taken in an enclosed space or if a plastic bag is used that covers both nose and mouth.
"Mixing nitrous oxide with alcohol is especially dangerous," the helpline says.
It can cause dizziness and heavy regular use can lead to severe vitamin B12 deficiency, which can cause serious nerve damage. Regular use also inhibits the formation of white blood cells and the immune system.
While the gas can be legitimately used for pain relief in dental procedures, in engines to make them perform better, and in aerosol cans to prevent food going off, there have been concerns at its use as a so-called legal high.