NBA players Ivica Zubac and Dario Saric were involved in an intense physical altercation at a nightclub near Athens, Greece early Monday morning ... just hours after the two competed for Croatia in an Olympic Qualifying Tournament game.

TMZ Sports has obtained video taken inside the popular Bolivar Beach Bar around 5:30 AM ... which starts with the LA Clippers big man already involved in a scrap with someone as several men -- who appear to be club security -- rush up and grab him from behind.

As the chaos unfolds, Saric -- who just agreed to a two-year deal with the Denver Nuggets -- bolts into the crowd to try and help Zubac ... but appears to get shoved by another staffer.

At one point in the scuffle, a man puts Saric in a chokehold and brings him to the ground ... where he laid for several moments. Meanwhile, a man is shown yelling at Zubac and telling him to calm down -- which worked, as he stepped backward with his hands up.

Eventually, Saric gets up and stumbles toward Zubac ... and the group of men push the hoopers to the exit.

Witnesses on the scene say it's unclear what sparked it all ... as it all broke out rather quickly. We're told it did not appear police were present.

Earlier in the day, Zubac and Saric suited up for Croatia's matchup against Giannis Antetokounmpo and Greece in the OQT finals ... with both having solid outings.

Zubac had 19 points and 13 rebounds in the contest ... and Saric added 14 of his own.

Croatia ended up losing the game 80-69 ... with Giannis and Co. punching their tickets to Paris.

We've reached out to Team Croatia for comment ... so far, no word back.