LAS VEGAS, Nevada: Manny Pacquiao is fighting mad and taking on Floyd Mayweather Jnr in court even as a potential blockbuster bout between the two is on the ropes.

Filipino hero Pacquiao filed a lawsuit in federal court in Las Vegas on Wednesday alleging that Mayweather and others defamed him by falsely saying Pacquiao used performance-enhancing drugs.

"Calling a professional athlete a cheater is the most serious charge one can make," the lawsuit says, "and in today's world, accusing an athlete of using performance-enhancing drugs - however baseless and lacking in evidence - is toxic."