Roy Keane has told footballers to play chess if they are worried about getting hurt.
Responding to a question about striker Kevin Doyle's retirement last week because of repeated bouts of concussion, the Republic of Ireland assistant manager admitted his sadness at the player's plight, but insisted that injury is an occupational hazard for professional athletes.
Keane said: "It's sad, but he's made the right decision, no doubt. He's had an excellent career and seems a real decent guy.
"It's sad to see him retire. He's 34, he's had a decent innings and hopefully he's picked the right time to retire. As everyone else has been saying, your health is your wealth.
"If he's had concussions over the years and he feels he's suffering from them, then obviously he feels that's right for him.
"But it's part of the game - players picking up injuries and getting knocks. He's a centre-forward, he's going to be running the channels with centre-halves - it's what you'd expect. I'm sure he's knocked a few centre-halves over himself and he's had a few knocks, and that's part of the game.
"There's risk involved in everything, particularly sport. It's a physical game. I think Kevin's picked the right time to say, 'Enough's enough'. We wish him well, of course."
Asked if more research needed to be done, Keane said: "I'm sure there is, that's ongoing. But if you're worried about the physical side of any sport, you're wary of it, then play chess.
"It's part of the game, whether it be hurling, football, American football, the rugby lads, it's part of the game.
"When you cross that line, there is an element of risk involved. I don't think it would make a difference to the players playing now. When you cross that line, there's a chance that you might get a knock.
"I'm pretty sure there is a lot of research going into it. People question the PFA, this and that, but when you cross that line, there's a chance you might get hurt. They're the risks you take."
The family of former West Brom striker Jeff Astle launched the Jeff Astle Foundation to campaign for better protection for modern players following his death at the age of 59 from a degenerative brain disease which has been attributed to repeated heading of the ball.
Concussion has also become an increasing concern in rugby union and American Football in recent years.
Brain injury association Headway stressed the importance of not taking any risks where concussion was concerned.
Peter McCabe, the chief executive of Headway, said in a statement: "Sport plays a key role in keeping us fit and healthy and it's important to address safety measures with a common sense approach that does not discourage people from taking part in sports that take a responsible approach to head injuries.
"There is risk in most things in life; the challenge is to fully understand and manage those risks appropriately.
"It is very encouraging that, for the most part, football is beginning to take the issue of concussion seriously and, along with more research, a cultural change is beginning to take place.
"It is vital that we continue to conduct more research into the potential long-term implications of heading footballs to ensure people are able to make informed choices.
"In the meantime, the focus has to remain on raising awareness of the importance of taking a safety-first 'if in doubt, sit it out!' approach to concussion."