Conor McGregor has come under attack again from former sparring partner Paulie Malignaggi for being "one of the biggest dirtbags I've ever met in my life".

Malignaggi quit the McGregor camp last week after photos were leaked on social media that suggested the Irishman had knocked down the retired boxer as he prepares to fight Floyd Mayweather Jr this month.

The much-publicised bout in Las Vegas will see UFC star McGregor go toe-to-toe with Mayweather - who has returned to the ring two years after leaving the sport with a perfect 49-0 record.

Malignaggi claimed McGregor "whimpers like a girl" when he is hit by body shots, and he continued his verbal onslaught by labelling the 29-year-old a "dirtbag".

"This guy is one of the biggest dirtbags I've ever met in my life - bar none," Malignaggi told MMA Hour.

"I was amazed at what a dirtbag this person is. I don't care if we never speak again. My life is fine if I never see Conor McGregor again.

"I was dumbfounded by the way things were. It's just about status with him. It makes me doubt if he ever really went through a tough time in his life like they try to say he did. If somebody went through that tough a time in life just a few years ago, they wouldn't treat people who were not as fortunate as him that bad."

Malignaggi also claims McGregor is scared of being challenged in the ring, something Mayweather is likely to exploit.

"He doesn't want to be put in those positions. He wants to be the front runner," Malignaggi added. 

"He wants to be the guy who always has the advantage, because when he has an advantage he's a big man. When he gets tired, he wants out of a fight."