Former Scotland footballer spoken about his time behind bars in a rare interview, claiming he should never have been sent there.
The ex-Rangers striker became the first and only professional player in Britain to be jailed for an on-field offence after he headbutted John McStay, the Raith Rovers defender, during a match at Ibrox in 1994.
The following year he was convicted of assault at Glasgow Sheriff Court and sentenced to three months.
He spent 44 days in the city's Barlinnie prison before being released.
However in a rare interview, Ferguson has described the headbutt as "nothing" and claimed he should not have been made an example of.
He was jailed only five months after winning the FA Cup with his new club Everton and the 47-year-old said letters from the Merseyside club's fans helped him get through his time locked up.
He said: "It was wrong me being there, it wasn't fair.
"I shouldn't have been in there and I think a lot of people understood that.
"It's not as if I was in for doing anything bad really. My God, it was nothing.
"The fans got me through it, a lot of them wrote to me. It was unbelievable all the letters and the support that I got.
"I got all the letters when I was in there and obviously you have got a lot of time on your hands when you're in there to read through them all.
"It definitely gets you through it and you never forget those things."
Speaking to Everton fans' channel Toffee TV, Ferguson said he grew a beard at the time as he wanted to look "tough" during his stint in the notorious Glasgow jail.
He added: "It made me look tough. When you're going to one of they hotels up there you've got to look tough."
Ferguson, who is now a coach at Everton and does community work for the club, also said his hardman reputation was unfair.
He said: "You get a reputation and you can't shake it off. It follows you around and it follows you around.
"I don't see myself as that person. I see myself as the person I see off the field and I try to give as much back as I possibly can to the city because it's gave me so much."
His prison sentence was for his third conviction for assault and saw him banned for 12 games by the Scottish Football Association(SFA) - leading him to refuse to play for the national team again.
Ferguson was born in Stirling and began his career with Dundee United, before moving to Rangers in 1993.
He arrived at Everton in 1994 and won an FA Cup medal the following year when they beat Manchester United 1-0.
Despite a career disrupted by injuries he was a cult hero on Merseyside.
In the interview, he blamed his injury-plagued career on breaking his big toe during a pub fight in Dundee when he was aged 18.
He said: "The first injury I ever had was when I broke my big toe.
"I broke it in a fight in a pub called The Rock in Menzieshill in Dundee.
