Paris - 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."
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.