England international Cahill was involved in a clash of heads with the former Hull City man in January 2017 that left Mason with a fractured skull.
The ex-midfielder was forced to retire earlier this week 13 months on from the injury, news which Cahill was "devastated" to receive.
"I was devastated to hear that Ryan Mason has retired from professional football this week, I can't even imagine what he's feeling and going through, having to retire at such a young age, and when I heard the news it was heartbreaking," the defender told Chelsea's official programme.
"I've got a son and a beautiful fiancee around me, so these are the sort of things that mean more to you than football when things are put into perspective. Challenging for the ball in the air is such a common thing and you never expect consequences like this to come from it.
"That is when football goes totally out of your thoughts and it becomes about making the best decision for your health. I want to spend my best wishes to Ryan and his family. The most important thing in life is your health, and I am sure he will now go on to be successful in whatever he chooses to do next."
Cahill wrote the comments after penning a tribute to the retired midfielder via Twitter on Tuesday.