The Hoops boss, who lost both parents to cancer in 2010 and 2011, took time out to contact the lifelong fan after being made aware of his plight.
Rodgers wrote: “Dear John, I have been made aware that you have recently been diagnosed with cancer.
“I understand that your support and commitment to Celtic Football Club over the years has been relentless and I wanted to drop you a note.
“I expect receiving this news has probably turned your life upside down and you are trying to find ways to cope with such a blow.
“There are few people that have not been touched by the terrible scourge that is cancer and I know that this must be an incredibly difficult time for you, your family, and friends.
“I know you have a difficult battle ahead and no doubt there will be many tough and trying times.
“You will be in my thoughts and prayers. Keep your spirits up.”
Fans of all clubs have praised the gesture, with Tomas O’Kane writing: “Absolute class. All the money in the world can’t buy that. A club like no other.”
Jaggy Thistle tweeted: “Not a Celtic supporter, but, well done. Nice touch.”
Rangers fan @stewbar added: “What a wonderful gesture” while Jim W said: “Class isn’t a big enough word.”