Justin, who played for Norwich and Nottingham Forest in the 1980s, came out before he took his own life in May 1998 at the age of 37.
As the 20th anniversary of his death approaches, John admitted he had acted like “a monster” to his older brother and now wants the Football Association to do more to support gay footballers and tackle racist and anti-gay abuse.
“It was a lack of education,” the former Wimbledon and Aston Villa striker told ITV’s Good Morning Britain show on Wednesday.
“I make it very clear I was a monster to Justin then. I paid him £75,000 not to say that he was gay.
“I was looking at the situation around us and my mother had cancer and was dying, and the rest of the family couldn’t understand the situation.
“We didn’t know what to do, the best thing I thought to do was to keep it quiet.”
Capped by England at Under-21 level, Justin was the first black footballer to command a £1 million transfer fee when he moved from Norwich to Forest in 1981.
He publicly came out as gay in 1990 and played for nearly 20 clubs before retiring from football in 1997.
There are currently no openly gay players in the Premier League, but ex-England international John said he knows of several “well-known footballers” who are gay and wants the FA to do more to support footballers coming out.
“We have a number of well-known footballers who are gay and they don’t feel comfortable with the environment,” he said.
“They know their empires will be destroyed. It is supporters, administrators … not so much the players, because they know who is gay and who is not gay.
“They give each other support, but it is quite gentle support.
“We are pushing the FA needs to create an environment where gay footballers are comfortable to come out and say: ‘I’m gay.’”
He said he had been a victim of racist abuse at a recent Premier League match and added, “A gentleman came up to me and said: ‘You black so-and-so and your brother’s this and this.’
“I was surprised – I hadn’t been to a match for a few years and I thought to myself: ‘Even at this stage.”
