The 30-year-old, who made 24 appearances for his country and over 400 for clubs including Doncaster Rovers, Sheffield United, Barnsley and Birmingham, said he had been battling the condition since his teens.
“I had an Aston Martin, the big house, anything a person could want – but you can’t help what’s in the brain,” said Cotterill in an interview with the BBC.
“It’s the most powerful tool you have and what you feel can block out everything you have. And when you’re fighting that battle every day, it takes its toll.
“I’ve searched for the easiest way to commit suicide.
“Then you think, how can you do that when you have children, a wife?
“You kind of then have a couple of days when you feel OK again, but then it will keep repeating itself.”
Cotterill, who is currently without a club after leaving Indian Super League side ATK in January, believes the extent of the issue in the game is largely hidden because of the demands and expectations placed upon players by both their clubs and managers.
“I don’t think you can go to the manager or club and say, ‘by the way I’m not coming in today, I’m going to see a doctor because mentally I’m not feeling great’. It’s not possible,” added Cotterill.
“I truly believe if a manager or club finds out they’d use it as a weapon to not play you. If you’re the big man or big dog in that football team you potentially might get help; if you’re just a number in that squad I don’t think you’re getting the help you deserve or need.
“If we’re trying to protect injuries, knee injuries, foot injuries, whatever it might be, then why are we not protecting the brain, I don’t get it.
“We definitely need to look into it.
“If everyone was open and honest (in football) about depression there would be a scary number. A huge number.”