Lamar Odom: Shady Friend Shows Up at Hospital ... Demands Access

Lamar Odom had a visitor Monday night ... a guy who claimed to be Lamar's assistant, insisting Lamar had summoned him ... but hospital officials smelled a rat.

Our sources tell us the guy arrived around 11 PM and got on Lamar's floor when security stopped him. He said Lamar had called him and he came down from Vegas because Odom was insistent on seeing him.

Our sources say the guy has a history with Lamar and Odom's people believe he facilitated Lamar's drug use. The 2 men lived together in Vegas at some point. We're told Lamar's management fired the guy the day Lamar went into the hospital.

Security was unbending and refused to let the man in. There was yelling and "a big scene" before he was escorted out.

Khloe was not at the hospital when it went down.