Saunders is due to defend his WBO middleweight title on Saturday night at the Copper Box Arena with the winner expected to make a claim to fight the winner of Canelo vs GGG, the other middleweight title fight taking place this weekend.
Monroe Jr has already been involved in one confrontation with Saunders as the pair shouted obscenities at each other in gym last week.
But they were better behaved as they weighed in on Friday, only for his son to aim a punch at the groin of Monroe followed by a kick in the shins.
He appeared unapologetic afterwards as security pulled him away from the American fighter and his father Billy Joe back him up in the aftermath.
“My son’s been taught when a stranger puts their hands on them…punch and run away – self defence,” Saunders tweeted afterwards.
Saunders and Monroe Jr are two of the middleweight divisions leading lights but their bout pales into insignificance compared to Canelo Alvarez’s clash with Gennady Golovkin.
Triple G, as he is known, is unbeaten in 37 fights with 33 wins by knockout and holds the WBA, WBC and IBF belts.
But Alvarez will be one of his stiffest challenges and the fight is already being billed as the boxing occasion of the year.
However, Saunders believes he is ready to step up to fight the best in the world and Golovkin appears ready to take him on – assuming Canelo doesn’t want to face him again.
“If the first fight is a barn burner and both guys want to do the rematch then we will see the rematch,” said Golovkin’s promoter Tom Loeffler.
“If GGG wins, and Canelo wants to take some time off then I could see the Saunders fight happening.
“Billy Joe is one of those guys that if he is in shape and motivated for a fight, he’s a terrific fighter.
“Unfortunately he does a lot more talking about fighting GGG than actually signing to fight him.”