Hull City midfielder Ryan Mason has been forced to retire at the age of 26 as a result of the fractured skull he suffered against Chelsea in 2017.
Mason, who won one cap for England in 2015, had to have surgery after a clash of heads with defender Gary Cahill.
His decision to retire follows "the guidance of numerous world-renowned neurologists and neuro surgeons".
He said he had "worked tirelessly" to play again but "the risks involved had given him no option but to retire".
Mason started his career with Tottenham and joined Hull for a club record fee, believed to be about £13m, in August 2016.
After eight minutes of treatment on the pitch during the Premier League match at Stamford Bridge in January 2017, Mason was given oxygen as he was carried off on a stretcher.
He had surgery at St Mary's Hospital in London, where he stayed for a week afterwards, and has since spoken of feeling "lucky to be alive".
Mason started training with the club again in May last year but no expected return date was ever given.
Tigers boss Leonid Slutsky said in August that "the question is not just about football but about his life" when the player went to see a third specialist.
The Championship club said in a statement: "Ryan would like to put on record his thanks to all at the club who have aided his recovery to this point and he is indebted to them for their support and compassion over the past 12 months."
Tottenham manager Maurico Pochettino, who Mason played under at Spurs, said "the door is open for me to help him".
"He is 26 but his brain is amazing, he is an amazing person," he said. "He will be a very successful person in football, in everything he wants to do. For me, Ryan is a player who will always be special.
"Don't worry Ryan, you are going to be a successful person outside the pitch."