Learning of Ryan Mason's premature retirement on Tuesday due to a head injury suffered in January 2017 was "heart-breaking" for Chelsea defender Gary Cahill.
Mason clashed heads with Cahill in a match at Stamford Bridge early last year and fractured his skull in the incident.
The midfielder was initially expected to return to football, but recent scans showed the injury to be even more significant than originally feared.
As a result, Mason announced his retirement on Tuesday at the age of 26 to an outpouring of tributes and well wishes from across English football.
Chelsea coach Antonio Conte said in his pre-match news conference ahead of Friday's match with Mason's former club Hull City that Cahill should not be blamed, but the centre-back cannot help feeling "devastated" for his former England team-mate.
"I was devastated to hear that Ryan Mason has retired from professional football this week," Cahill wrote in his notes for Friday's match programme.
"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 heart-breaking.
"Ryan is a lovely guy. I've met him and trained alongside him with England, and it's a horrible situation. 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 you health.
"I want to send 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."
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