Neymar is expected to face a two-game ban for slamming the penalty decision given to Barcelona on Tuesday.
The Brazilian star could be made to explain his tweets during the 4-1 win for his PSG side.
And Uefa could act with a ban of up to two games for the 29-year-old.
The UEFA disciplinary code stops players from ‘insults or other conduct that violates the basic rules of conduct’.
Neymar was given a three-game ban in March 2019 for insulting match officials, but it was reduced to two by CAS.
He missed Tuesday’s thrilling Champions League last 16 first-leg tie through injury.
But Neymar was active on Twitter after Frenkie de Jong controversially won a penalty for Barcelona in the 27th minute.
It appeared the Dutchman may have just tripped over his own legs, but that didn’t stop the ref from awarding a penalty against Layvin Kurzawa.
A VAR review sided with the match official.
Neymar tweeted: “Joke that penalty,” accompanied by laughing emojis.
And former Nou Camp pal Lionel Messi stepped up to calmly put Barca 1-0 up.
The tweet was quickly spotted by fans, who shared it on social media.
But it wasn’t live for long, with Neymar deleting it.
However, it was PSG who had the last laugh in Catalonia.
Kylian Mbappe scored a magnificent hat-trick as the French side ran out 4-1 winners.
The 22-year-old striker’s performance was lauded by BT Sport pundits Joe Cole and Rio Ferdinand.
Ex-Man Utd defender Ferdinand said: “Mbappe is on his own – out of young players he’s on his own. People forget he’s 22 years old.
“Given he’s won the World Cup, what he’s done in the French league and in the Champions League, he’s been immense.
“I just feel that he’s the guy now that’s going to take the throne, take the crown, he’s standing alone at the moment. It’s for everybody to catch up to him now.
“This guy is going to take over the throne from Messi and Ronaldo when they’re done with it.”
And former Chelsea midfielder Cole said: “[Mbappe] is the best player in the world, at the moment.
“The influence he has on his team, the way he can just run away from players.
“His link-up play, his work-rate off the ball… he is the alpha dog in football at the moment.
“The top player in my opinion – maybe Ronaldo still. But as young players go, if you want to build a team, go and get Kylian Mbappe.”