Rick Ross -- Ex-Groundskeeper's a Liar ... I Never Pistol-Whipped Him

Rick Ross is attacking the groundskeeper who is suing him for allegedly pistol-whipping and beating him ... but this time, Ross is admittedly attacking with a gun ... a hired gun.

Ross has filed legal docs against Jonathan Zamudio, who sued Ross claiming the mogul got angry at him for throwing a party in his mansion and driving his cars. Zamudio says Ross locked him in a room, pistol-whipped him and brutalized him so bad he had to eat through a straw.

But Ross now says Zamudio is lying ... and claims he has proof. For starters, Ross notes Zamudio called 911 THREE HOURS after the alleged incident and never mentioned pistol-whipping or any injury for that matter. He also spoke clearly and calmly to the dispatcher.

Secondly, Ross says Zamudio is in cahoots with his arch enemy, 50 Cent. You'll recall Ross' baby mama sued 50 for posting a sex tape featuring her on his website. A jury felt 50 did it maliciously and awarded her $7 million. Ross says Zamudio's lawsuit is really just 50's revenge.

Ross points to a photo 50 posted of himself with Zamudio, along with the caption, "Now you pay."

Ross calls this a simple shakedown from a guy who left paraphernalia used for cocaine and other drugs all over his house.

Ross was arrested and jailed in connection with the incident and charged with kidnapping, aggravated assault and aggravated battery. That case is pending and Ross is free on $2 mil bond.