The Austin-based attorney tells TMZ that Nelson -- who was picked up by police Friday in Sierra Blanca, Texas, (which is 30 miles from the Mexico border) after they smelled the drug on his tour bus at a checkpoint -- could face a minimum of six months in jail.
Bruce Margolin, director of the L.A. chapter of NORML, which fights for marijuana legalization, says Nelson could skip jail time if he is able to convince he forgot he had the Calfornia-grown drug on the bus, and it was for medical use.
This wasn't the first drug arrest for Nelson, who was released Friday after posting $2,500 bond.
In 2006, he was arrested with 1.5 pounds of marijuana and three ounces of hallucinogenic mushrooms on his tour bus. In 1995, he was arrested in Waco, Texas after police spied half a joint in his car's ash tray.