The Irishman joined City and played for the youth team and reserves but with only a few outings on the bench, he was released by Gordon Strachan in 1998.
Recently, Costello finished joint top of Powerade PGA Assistants Championship in County Meath to get a shot at £5k in the final at East Sussex National on July 28th and he told the CT's Andy Turner: "I wasn't enjoying it to be honest and when I was released by City, I just lost interest. But I did get to work with Ron Atkinson who is an absolute legend and a great guy.
"We all used to love the crack with Big Ron, especially the five a sides where he'd join in and shout for the ball, saying: "Give it to your best player".
"I have always loved my golf but didn't join a club until I was in my early twenties. So I was a bit late to it. Now I'm taking the PGA route and this is my first year and I'm new to the Powerade event so I was pleased to qualify for the final."