The club's third most capped player announced his exit from professional football on Wednesday to pursue a life away from the game. A move that stunned several members of the Sky Blues' squad.

It's understood Ryall turned down the opportunity to play for rival A-League clubs as he didn't want to play against Sydney FC - the club he made 168 A-League appearances for - and was not interested in playing in South East Asia.

His departure leaves Sydney FC with only three central defenders ahead of a busy end to the season. The club will have to balance the A-League with their Asian Champions League campaign.

Youngster Aaron Calver is the only replacement for first-team pair, Jordy Buijs and Alex Wilkinson, who has A-League experience. Patrick Flottman from their youth team is yet to make his debut.

"[We've got] plenty of depth and cover there but, of course, naturally it's disappointing to lose him," Sydney defender Luke Wilkshire said. "It's a shock and it is obviously disappointing for us to lose such a person and player but in life things go beyond football."

Ryall requested a release from the last 18-months of his contract and will likely spend some time overseas away from the game.

"I think it's great the club have dealt with it the way they did, allowing him to pursue his wishes. Personally, I had contact with him as well and wish him all the best," Wilkshire said.

While Ryall's departure leaves a hole in terms of depth for Sydney FC, the club is boosted by the return of Rhyan Grant to full-training after a lengthy absence due to a ruptured ACL.

Winger David Carney was the only player absent from training on Thursday, though the club suggested that was because of illness rather than recent legal issues.

The former Socceroo was given a day's rest after reporting a gastro illness, a day after he was scheduled to appear in Belmont local court for traffic offences for a mentioning of a charge of driving while his licence was suspended. He is set to reappear in court on January 31 and is expected to return to full training on Friday and remains in contention to face the Mariners on Saturday night. The club declined to comment on the incident.

Meanwhile, Central Coast Mariners have bolstered their stocks for their visit to Sydney with the signing of Peter Skapetis from Brisbane Roar. The 23-year-old is a former Australian youth international and is a chance to make his debut for the Mariners at Allianz Stadium after being granted a release from Brisbane.

"Peter is fit and ready to go," Mariners coach Paul Okon said. "He will add to our depth in the front third as he can play anywhere in attack."