Ryan Mason has revealed that his decision to retire from football was made after a recent CT scan revealed "an issue in the brain that wasn't shown before".
Mason was hospitalised for over a week and left with 14 metal plates in his head after fracturing his skull in a clash of heads with Blues defender Gary Cahill.
Although Mason had been working towards a comeback, the CT scan showed that the injury's effects were more serious than had previously been realised.
"It's been no secret that I've been 100% determined to get back," the former Tottenham Hotspur player told talkSPORT.
"But a few weeks ago I had a follow-up CT scan and it revealed an issue with the brain that wasn't shown before.
"I've sought about 10 specialists' advice, but the risk was too high. To think about heading the ball if I needed to, it just wasn't realistic.
"I have come to terms with it. I feel good about the situation now. I've gone through that emotional side of it, of having to accept I won't be playing again.
"The decision was taken out of my hands, so I know I'm not going to regret anything further down the line. There's a lot of relief on my family's part.
"Now I can look forward. The next chapter of my life is going to be an exciting one."