Manolo, 20, grew concerned about his mother's relationship after Loeb dragged Vergara into an ugly melee at a Miami Beach nightclub, reported the National Enquirer.
"Nick's hair-trigger temper has Manolo scared to death. Manolo desperately wants to like the guy, but violence seems to follow Nick around," said a source.
"Manolo is extremely protective of his mother, and now he's afraid for her safety. He believes Sofia should slam the brakes on her wedding plans immediately."
Problems started after Loeb, a 37-year-old businessman and banking heir, rang in the new year with Vergara, 40, and Manolo at the Delano hotel in Miami's trendy South Beach.
"Fortunately, Sofia wasn't hurt. But Manolo was worried that she could have been. And, next time around, she may not be so lucky.
"Manolo accepted Nick only because his mom's in love with him. He wants her to be happy. But he was never crazy about Nick