Nelly -- Not My Meth ... Challenges Drug Arrest

Nelly's lawyer is already mounting a defense in his meth arrest Saturday, claiming the drugs found weren't his.

Nelly was arrested on his tour bus in Tennessee after it was pulled over for not having proper stickers. Cops say they smelled pot, then searched the bus and allegedly found meth, marijuana and guns.

Nelly's lawyer, Scott Rosenblum, tells TMZ there were 15 to 20 people who had access to the bus prior to the stop and there were multiple people on the bus when cops searched it. Rosenblum seems to take issue with cops on the meth issue saying, "a small quantity of [MDMA/Ecstasy] was discovered."