Zac Efron -- Nearly DROPPED $100K Gift Bottle of Champagne

Zac Efron almost committed the biggest party foul EVER – dropping a $100,000 dollar bottle of “Ace of Spades” champagne ... his baller gift from a Russian billionaire's son.

Sources inside Board Room nightclub in Chicago tell TMZ ... Zac attempted to lift the full 15 litre bottle on Tuesday night. We're told Zac learned the hard way it was too heavy for him -- but managed to hold on just long enough to avert the ultimate disaster.

Note: The massive guy pictured (above) delivered the bottle without breaking a sweat.