Mason suffered a fractured skull when he collided with Cahill during a match at Stamford Bridge in January 2017 and has been unable to play since.
The ex-Spurs midfielder had looked like completing an unlikely comeback in recent months, as he had returned to training with Hull City at the beginning of the season.
However, Mason has now conceded he has been be forced into retirement, admitting he had “no option” but to hang up his boots.
Cahill has since taken to social media to address the 26-year-old’s decision, calling it “heartbreaking” and wishing Mason “the best for the future”:
Devastated to hear today’s news from Ryan. Competing for a corner is something we’ve done thousands of times and to see those consequences for a top professional like Ryan is heartbreaking. Sending all my love to him and his family, and wishing him the best for the future.
— Gary Cahill (@GaryJCahill) February 13, 2018
In an official statement, Mason said, “I have worked tirelessly in order to be able to return to the pitch.
“Unfortunately, having taken expert medical advice I now have no option but to retire due to the risks involved given the nature of my injury.”
It’s unclear at this stage what the future holds for Mason and whether he will stay in the game in a non-playing capacity… but we certainly wish him all the best!