Finch, who was fielding at short leg, was struck on his helmet when Steve O'Keefe played a flick off James Pattinson during the first session on Day 2 of the match.
The 33-year-old was assessed on the ground immediately and continued fielding after he was cleared by doctor Trevor James. However, Cricket Victoria said he experienced ‘delayed concussion symptoms’ during the Lunch break.
Dean, who replaced Finch, was batting for his Premier Cricket side Footscray at Windy Hill in Melbourne's north-west when he was told he needed to retire his innings and drive to the MCG.
The concussion substitute rule has been in place in the Sheffield Shield since the 2017-18 season and was introduced into international cricket earlier this year, with Marnus Labuschagne becoming Test cricket's first replacement player when Steve Smith was hit on the helmet by a ferocious bouncer by Jofra Archer during the Ashes.
In 2014, Australian batsman Phil Hughes had passed away at the age of 25 after he was hit by a bouncer in a Sheffield Shield match between South Australia and New South Wales at the Sydney Cricket Ground. He was wearing a helmet, but the ball struck an unprotected area just below his left ear.
Hughes sustained a brain haemorrhage and died two days later without regaining consciousness at a nearby hospital.