Long-serving Central Coast A-League utility Brad Porter has called time on his playing career due to an ongoing injury.The 25-year-old defender, who made his A-League debut in 2006/07, spent more than six years with the Mariners, making in excess of 90 competitive appearances.Porter suffered a serious knee injury in the 2010/11 season and has struggled to make a full recovery since."It's been a tough decision to make to have to retire from the game but, at the end of the day, I did the injury nearly two years ago now and, in that time, it's been extremely frustrating trying to come back and having setbacks," Porter said."The way I look at is that I've been a professional at the club for close to seven years and there are a lot of young kids and a lot of people out there that would give up a lot to have done that."I'm very proud of what I've achieved at this club."To have been here from basically day one and to have seen the growth of the club both on the pitch, and building the supporter base and the community support, has been unbelievable."Porter said he would pursue a career as a coach and plans to spend time around Graham Arnold's squad to gain experience.Arnold described Porter's retirement as a tragedy."We wish Brad, as a guy who is a Mariner through and through, the best for the future," Arnold said.