Lamine Yamal said 'this can't be recorded' while on Instagram Live following Barcelona's Supercopa de Espana final win over Real Madrid.
Barca won the match 3-2 in Riyadh.
Hansi Flick's side twice took the lead in the first half through goals from Robert Lewandowski and Raphinha, before Real hit back on each occasion through a superb solo goal from Vinicius Junior and then young Spanish striker Gonzalo Garcia.
Raphinha scored his second goal and what proved to be the winner on 73 minutes.
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Frenkie De Jong was then sent off in second-half stoppage time to briefly put Barca under intense pressure, but they held on to secure their first trophy of the season.
Yamal was not directly involved in any of his side's goals, but did play 93 minutes before being substituted as Barca looked to protect their lead.
The 18-year-old took to Instagram Live to film some of his side's dressing room celebrations.
But he inadvertently flipped the camera at one stage during the recording, with several of his team-mates appearing in shot.
Goalkeeper Wojciech Sczezsny could be seen appearing to smoke, at which point Yamal flipped the camera back around before stating: "Woah, this can't be recorded!"
Former Arsenal and Juventus goalkeeper Sczezsny has previously been open about his smoking habit, warning young players not to follow the same path as he did.
Speaking to ESPN in April, he said: "There are some parts of the game where I believe I can be a perfect example for young people, or in fact, for my team-mates. And there are some things in my career that you better not follow.
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"In a few aspects, I fail at, but I try to give the correct example to my team-mates, to young kids who watch us.
"But mentioning the subject of smoking, please do not follow me and don't do it.
"I've lost the fight. When I was very young, I created a habit that is very negative for me, and I know it is. I just lose against it.
"So for anybody watching: Don't do what I did."
Topics: Lamine Yamal, Barcelona, Real Madrid, Football
Ryan Smart