Modern Family star Ariel Winter's mum is suing actor Matthew Borlenghi for defamation after he allegedly branded her an "abusive monster".

Chrystal Workman's lawsuit, filed in Los Angeles Superior Court on Monday (10Dec12), stems from a comment Borlenghi is said to have posted online in response to a Los Angeles Times blog story detailing the teen star's family drama.

The article included an allegation by Workman that her daughter's 18-year-old boyfriend had unlawful sex with the 14-year-old actress.

According to the suit, Borlenghi wrote in response, "This is a total falsehood. The mother is grasping and clawing to find a way not to lose her money-maker, and hide the fact that she is an abusive monster. Having spent time with her, and seeing the way she acted adoringly towards the boy, (these) accusations are disgusting, just as she is."

Workman refutes Borlenghi's allegation in her complaint, which seeks unspecified damages and suit costs.

Winter, who plays Alex Dunphy on the Emmy Award-winning show, was placed in the care of her older sister Shanelle Gray after accusing her mum of subjecting her to emotional and physical abuse.

A trial to decide whether Workman will permanently lose custody of Winter is scheduled to start on Wednesday (12Dec12).