The 25-year-old soccer superstar spent his Tuesday floating off the coast of Brazil with his smokin' hot girlfriend ... and some of his PSG teammates, who also have model GFs.

See the butt in the main image? That's Victoria's Secret model Izabel Goulart -- who's dating Neymar's Paris Saint-Germain teammate, Kevin Trapp. Kev was there, too.

But the big story is Bruna Marquezine ... Neymar's on-again, off-again lady friend who's been fully BACK ON with the soccer superstar going into 2018.