This was rare for the times. How could a superstar footballer earning that much money and with that much adulation from fans be suffering with a mental illness?
Since then, the 42-year-old has made it his mission to inform others about the condition by being as honest and unabashed as he can be.
The former England international has recently helped the charity Depression Alliance launch a new initiative called Friends in Need - an online and offline community that aims to help end the loneliness and isolation that nine out of 10 people suffering with depression are affected by.
Here, Sports Mole speaks with the former England international about his personal experiences and how depression fits into football as a whole.
How big a taboo does depression remain in football?
"I think in football now it's not a big taboo at all. I spoke out in 1998 and I went to a clinic in Roehampton. When I came back to the dressing room, my teammates were saying 'where the fuck have you been?', so I told them that I had been having treatment which may well save my life, and they were like 'really?' And the irony is that one or two of those players in that dressing room went on to have issues themselves. I've spoken to them since and they've said that they didn't understand at the time, but then real life kicks in at some stage.
"Nowadays we've seen the cricketers Michael Yardley and Marcus Trescothick, numerous other sportsmen who have come out and spoken about depression - so I think that it's understood and accepted as an illness like any other.
"In a dressing room with 25 guys, you're always going to have one or two who say it's bollocks. It's changing, though, because, for example, I don't get as many people on Twitter as I did three or four years ago saying that depression doesn't exist. There has been a massive sea change in opinions."
Does football, and sport in general, have a bad reputation for lacking acceptance when it comes to things like depression, racism and homophobia?
"Yeah, I think football gets bad press on many, many levels but we tackle depression head on, we tackle racism head on by virtue of the fact that the Football Association and the Premier League will survey the Professional Footballers' Association and find those people who are having, or have had, serious problems.
"I think the way that football deals with issues is way, way ahead of other industries. People in other industries are terrified of telling their boss (if they have a problem), but I wasn't terrified of telling my boss back in 1998. My boss said to me 'I don't believe that a footballer earning this can have a problem', but then it started the debate. It made his argument look a bit silly. It's almost like you can have cancer, but you can't have depression.
"A lot of industries are still about being macho, about rolling your sleeves up, pulling you socks up, and we're still losing way too many people in certain industries because of a reluctance to speak out. So, yeah, football is doing plenty."
Was it Doug Ellis and John Gregory at Aston Villa who told you to pull your socks up when you came out with depression?
"Yeah. I remember when I opened up, The Sun newspaper said something along the lines of: To all Aston Villa fans - drive this man out of your club. Just because I had the audacity to come and speak out."
Would you say that your tendency to move around from club to club had anything to do with your depression? Was it a case of trying to start over each time?
"It's nothing I've ever really thought about in terms of depression. Maybe there is a link, I don't know. Maybe just in terms of my personality in general. I found it hard to get into the team at Crystal Palace; I was at Nottingham Forest for a couple of years before Liverpool came in with an offer; I was at Liverpool for two years but in the second year I had wind of the fact that Aston Villa were interested in me - they were my boyhood club. I was at Villa for four years and then I went to Leicester. Maybe there is something there but I think it's a greater personality issue. I certainly wouldn't use depression as an excuse that I wanted to keep freshening up."
At which club were you most happy during your playing career?
"All of them really. When you play well at a club, people assume that's where you were happiest but, generally speaking, they were all enjoyable clubs."
The experience at Aston Villa must have been difficult, though?
"To go to a club that I supported as a kid and am still very passionate about and not to have a good experience there would have compounded all of the things that were going on at that time. Looking back on it now, I'm still glad I made the move and played for the club. There were highlights - I'm only one of three players to score a hat-trick in Europe for Villa, we had some great European nights - and I would much rather have had that than not at all."
At which club would you say your teammates were most accepting of you?
"Leicester City, ironically. Here was a club that had lots of alpha males. You had Neil Lennon, Steve Walsh, Muzzy Izzet, Emile Heskey, Tim Flowers, Gerry Taggart - they were a lot of strong characters. By the time I got to Leicester, they all knew what I had gone through and they were all very chatty. Neil Lennon later came out and said that he'd been struggling with depression. The changing room that was meant to be very alpha male turned out to be the most supportive."
You've said that your family has a history of mental illness, but was it still difficult opening up to them about it when you were first struggling?
"Yeah, I remember I used to sleep for hours and hours and I would be awake during the early hours of the morning because I knew that nobody else would be up then. That's the closest I've come to it being like a daily nightmare.
"I would be physically flat, mentally flat, anxious. I wasn't eating right, wasn't taking care of myself, I wasn't seeing people, I wasn't engaging with people. And that's when you get to 'well, what's the practical solution to this? I know, I'll chuck myself off a bridge or I'll hang myself.' When people think like that, it's not a cry for help. It's a reaction to a day in, day out, fucking turgid flat mess that goes on and on and makes you unable to spread joy to your children or to your family or friends. It just becomes a nightmare. Literally nothing's going on.
"I've spoken to many people in the same situation and it actually gets to a point where suicide becomes a fantasy. If I do it then it stops, and if it stops then that's got to be a good thing. Then, of course, the things that bring you back are your kids, your relationships, your family. But when people say suicide is selfish, it's not. It's literally what people do when they're at the end of the line and their brain and body can't take anymore."
How else does your depression manifest itself?
"Two or three weeks before I get a bout I get very anxious. You're just like a cat on hot bricks for no good reason. A lot of studies have found that women tend to suffer from anxiety and insomnia, while men flit in and out of insomnia and have physical health issues. I was breaking sleep records. If I could have slept for three or four days, then I would have done."
What do you make of all the negativity that you get on Twitter?
"It doesn't bother me. People think that negativity spilled my way means that leads to depression. It's a fact that there are triggers to depression in some people. For me, the abuse I get on there has no connection. It doesn't work like that. I wouldn't have been able to play professional football with all of the abuse that comes with that."
Friends in Need is a new initiative from Depression Alliance to end the loneliness and isolation of depression. Stan Collymore is a founder of this initiative, and raised the initial funds to set it up. You can find out more at https://friendsinneed.co.uk/