The incident involved two current Victorian Liberal MPs, a man and a woman, according to newspaper reports.
Victoria Police confirmed officers are investigating an alleged assault at an event in Sunshine West on May 23.
"It was reported a woman was assaulted by a man at an event held at a function venue on Sommerville Road," police said.
The woman left following the incident and did not require medical attention.
She reported it to police on June 16.
The allegation comes five months out from the state election, where the party is attempting to turf out a three-term Labor government but also faces a surging One Nation.
It has been rocked by a series of scandals, including former deputy leader Sam Groth leaving his Mornington Peninsula seat of Nepean.
The first-term MP said the public pressure placed on his family had been significant, claiming that some of that had come "within my own party".
Meanwhile, a battle in the courts is continuing after Liberal MP Moira Deeming successfully sued former leader John Pesutto for defamation after he implied she was associated with neo-Nazis.
Mr Pesutto was ordered to pay $2.3 million in legal costs to Mrs Deeming and faced bankruptcy, which would have forced him from parliament.
The state Liberals' administrative committee agreed to loan Mr Pesutto $1.55 million, but committee member Colleen Harkin and four others on the committee sought to block the payment over an alleged breach of party rules.
They launched a Supreme Court challenge, which remains active.
Ms Harkin has since defected to One Nation.
Mrs Deeming was also ousted in preselection in her Western Metropolitan upper house seat before she was sensationally re-endorsed unopposed.
Successful challenger Dinesh Gourisetty was forced to step aside for previously providing a character reference for a now-convicted child sex offender.
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