In photographs posted to social media, Mr Guy and his MPs were snapped with Essendon legend Kevin Sheedy not wearing masks inside parliament on Tuesday, the first sitting day of the year.
The four-time VFL and AFL premiership coach, who coached the Bombers for 27 years, gave an unpaid motivational speech to the Victorian Liberal party room ahead of the 2022 state election in November.
Those in the photos include Mr Guy, upper house Liberal leader David Davis and Nationals MP Melina Bath.
"Victoria Police is currently assessing images circulating on social media of MPs without a mask on in parliament on 8 February," the force said in a statement.
Wearing a mask is required in all Victorian workplaces, including state parliament unless rising to speak in either chamber or eating or drinking.
A Parliament of Victoria work health and safety memo sent on Tuesday reminded MPs and staff of "the continuing requirement for masks to be worn in the workplace".
An opposition spokeswoman said in a statement: "Given police are 'assessing the images', we won't be providing comment."
Premier Daniel Andrews was fined $400 in October last year after he was filmed arriving at parliament not wearing a mask on two occasions.
He wore a mask on both days as he was driven to parliament but took it off before he walked through the car park to awaiting media.
At the time, Melbourne residents aged over 12 needed to wear a fitted face mask whenever they left their home, indoors or outdoors, unless a lawful exception applied, such as for broadcasting purposes.
