Neymar failed to show up for pre-season training with Paris Saint-Germain on Monday with the club announcing they would take "appropriate action".
In a terse statement, the French champions noted: "On Monday 8 July Neymar da Silva Santos Junior was due to return to pre-season activities with the Paris Saint-Germain senior squad.
"Paris Saint-Germain notes that Neymar Jr was not in attendance at the agreed time and place. This was without the club's prior authorisation.
"The club regrets this situation and will therefore take appropriate action."
In Rio, Brazilian media quoted Neymar's father as saying that PSG "were aware" the striker would be absent.
"The reason (for his no-show) was known and planned for a year as part of his activities for the Neymar Institute (charity foundation)," said Neymar Senior.
He added: "We couldn't postpone them and he will return (to PSG) on July 15.
"It's as simple as that, no drama. PSG are aware and take part in the Institute's activities."
Neymar left Barcelona to join Paris Saint-Germain for a world record fee of 222 million euros ($252 million) in August 2017, but could make a surprise move back to Camp Nou this summer.
Last week Barcelona's vice-president Jordi Cardoner told a press conference: "What is correct, at the current time, what I have read, what I have heard, which seems exact, is that Neymar wants to come back to Barcelona."
And media reports have indicated that intermediaries between PSG and Barca had hammered out the terms of a deal which would free the Brazilian star to return to his former club.
Spanish sports newspaper Diario Sport claims a five-year contract has been agreed.
The newspaper said last week the terms include Neymar reducing his salary from around 36 million euros at PSG to the 24 million euros he received at Barca in 2017.
The 27-year-old had spent four years at Camp Nou, winning the Champions League in 2015 and two La Liga titles. He had formed a brilliant attacking trio alongside Lionel Messi and Luis Suarez.
Any return for Neymar would likely require Barca to raise funds through sales. Frenkie de Jong has already signed for 75 million euros from Ajax. Antoine Griezmann is expected to join from Atletico Madrid for 120 million euros, although that deal has hit snags.
On Sunday, Griezmann failed to show up for pre-season at Atletico and the Spanish club, like PSG, threatened to punish their star striker.
Neymar's time at PSG has been punctured by injury and controversy.
He was questioned by Brazilian police last month over allegations he raped a woman he met through social media in a Paris hotel -- charges he has denied.
And the Brazilian star will miss three Champions League matches next season as punishment for insulting a referee following Paris Saint-Germain's Champions League collapse against Manchester United.
Paris Saint-Germain president Nasser Al-Khelaifi has warned Neymar and his other highly-paid stars that they must shape-up or ship out, claiming "celebrity behaviour" at the French champions will not be tolerated.
"The players will have to assume their responsibilities even more than before," Al-Khelaifi told France Football.
On Sunday, injured Neymar was watching from the stands as Brazil beat Peru in the Copa America final at Rio de Janeiro's Maracana stadium.