Collymore called his £7m move to boyhood club Villa in 1997 “a disaster” in his open letter, and highlighted some of the issues facing many young footballers.
He told 5 live: “What happens with younger players, and I have seen it at various clubs, is that they are a target. A magnet. People want to get into places on the back of them, want to sell them stuff, want them to supply a lifestyle.
“These young players have a lot of disposable income and they end up paying for holidays, paying for trips, weekends away. I’ve seen it, lived it, breathed it.
“It’s very difficult when you have 20 or 30 people around you saying nice things, being nice to you, to look at the motives of every single person around.
“What Jack needs to do is be like Michael Owen when he broke on to the scene. Do the boring stuff, have a game of snooker, have a cup of coffee, play a computer game – become boring.
“If you go down the other route then you get a reputation and it becomes very difficult to be a professional footballer.”
Grealish, 21, is currently the subject of an internal investigation by Aston Villa, whose new owner Tony Xia contacted Grealish directly via the social media platform Twitter on Wednesday, saying: “As I said before, focus every minute, on and off the pitch, choose the right people to be with.”
Players’ union the Professional Footballers’ Association is just one of the organisations able to offer support to players, but Collymore – who retired at the age of 30 – thinks senior players in the dressing room should take more responsibility.
“Some players would say it’s not their responsibility to mentor or babysit,” he said.
“But with young players and young people, it’s the responsibility of players and former players to get involved.
“These are not only famous footballers but impressionable young people.”