Smith last played in round 21 last season, before undergoing surgery to repair his hamstring.
Since then, Smith has struggled to regain full fitness, and has surgery once again in May, but still hasn’t returned to full training.
“Nick’s rehabilitation has been interrupted due to ongoing issues with his hamstring. While the initial signs following surgery in May were positive, Nick has been unable to return to full training,” Sydney’s Head of Football Charlie Gardiner told the club’s website.
“After seeking further medical advice over the last few days, it’s been decided that the best way forward is for Nick to undergo further surgery.
“It’s incredibly disappointing for Nick and for us, as he is a key part of our defensive group and an outstanding on-field leader. He has worked tirelessly in his rehabilitation over the past 10 months and we were hoping to have him back playing in the second half of the season.
“While he won’t play again this season, Nick remains an important part of the leadership group and will continue to assist in developing our young players.”
According to sydneyswans.com.au, a decision on Smith’s playing future beyond 2019 will be made later this year.