Sam Lutfi -- Britney Spears' Dad Threatened to Kick My Ass

Britney Spears' father Jamie Spears sent a text message to Sam Lutfi back in 2007 ... threatening to beat the crap out of him so badly, he'd wind up in the hospital ... so says Lutfi.

Lutfi is on the stand in his defamation case against Britney and her family ... and has asked the judge for permission to use the text message as evidence in the trial.

According to Lutfi, the text reads, "If and when I met u one thing is going to happen I am going to jail and u r going to the hospital."

The judge has not decided whether or not the jury will be allowed to see the text.

During today's hearing ... Lutfi says Jamie made good on his threats and attacked him at Britney's house. Lutfi claims Jamie punched him in the solar plexus and threatened to kill him.

Sam says he eventually locked himself inside a game room to get away from Jamie.