Young Buck got caught with his pants down.

The G-Unit soldier is required to provide urine samples every month as a condition of his probation for weapons charges. But during his drug test last week his probation officer spotted Buck funneling a yellow substance into his piss cup.

Buck tried the old second hand smoke excuse for why he was trying to cheat the test. But when that was sneered at he admitted he wasn't able to resist the urge of inhaling some weed with Snoop Dogg earlier this month.

Now it's up to a judge to decide if Buck's probation is revoked and he's sent back to jail.

As for Snoop being a bad influence ... the Doggfather recently implied that he had similarly made the most powerful man in the land succumb to his drug of choice.