Video footage appears to show the Brazilian running towards new boy Nelson Semedo and launching kicks in his direction before Javier Mascherano and Sergio Busquets step in to calm the situation.
Neymar could then be seen removing his bib and storming off the pitch.
Training is believed to have carried on in his absence though the it is fair to say that his team-mates will not have been impressed by his act of pettineess.
All the noises coming out of the Catalan club had suggested that the 25-year-old was happy to stay at the club this summer, with the player in fine form in pre-season with 3 goals in 2 games so far.
However, this action may be the final straw for Ernesto Valverde. It is understood that concerns have been raised in the past by the club over Neymar's lifestyle but the club were prepared to put up with it providing he did his talking on the pitch.
With the prospect of €222m in their pockets and one less troublemaker in the squad, they may now be tempted to cash in.
The walk-out comes just hours before Barca's pre-season friendly against Real Madrid.
'Sky Sports News' reports that the player is desperate for his move to Paris to go through in order to allow him to step out from Lionel Messi's shadow.
Ojo! Neymar peleándose con Semedo...Aquí tenéis el vídeo dónde se ve que Neymar le busca para pelearse. Tremendo. pic.twitter.com/p0x8zsiUn8
— Iván (@iblante) 28 de julio de 2017