Stewart started his career with Rovers after being born in the city, racking up 171 appearances, scoring an impressive 57 goals during that time.
Stewart returned to Bristol when he joined the Robins in 2005, making 27 appearances, scoring five times.
The now former striker finished his career with Exeter City in 2011 after a three-year spell, also spending time with Yeovil Town before that, and he has since returned to the Glovers to take up a coaching role.
But on Tuesday, Stewart confirmed in a statement that he has been diagnosed with Motor Neurone Disease, which affects the brain and the nervous system.
Stewart had been undergoing testing for 12 months prior to his diagnosis, and he spoke about the news in his statement, which was released with the PFA.
The former frontman said: “I would like to take the opportunity to thank those closest to me for their unwavering support since my recent diagnosis.
“As I take the time to adjust, my intention is to continue to enjoy my work in football and spend time with my family.
“In the future, I would like to use my platform within football to help raise awareness around MND, but in the short-term, I would like to ask for privacy on behalf of myself and my family.”
Following his diagnosis, Stewart and his wife Louise set up a JustGiving page with all proceeds going to the Darby Rimmer MND Foundation.
You can support and donate to the cause here.
Both City and Rovers have since posted messages wishing Stewart the best.
Rovers wrote on Twitter: “Our thoughts are with you and your family, Marcus,” while the Robins tweeted: “Everybody at Bristol City is with you Marcus.”