Fairfax Media understands Sydney FC received a letter from their fiercest foes on Wednesday night confirming the Wanderers' intention to submit offers to three members of their championship-winning defence who are coming off contract at the season's end.

The Wanderers have already turned their attention to the recruitment for next season and a number of players from Moore Park have risen to the top of their shopping list. Sources confirmed the players in the cross-hairs of Western Sydney are Sydney FC's central defensive pairing of Alex Wilkinson and Dutchman Jordy Buijs, as well as fullback Michael Zullo.

Buijs and Wilkinson were the backbone of the Sky Blues' A-League title-winning team last season, setting a record for the most lean defence in the competition's history. The pair have picked up where they left off last season, ensuring Sydney FC have the best defensive record thus far in the 2017-18 season, conceding only eight goals.

The Wanderers are also understood to be in pursuit of Zullo, having expressed their interest in writing to Sydney FC. The 29-year-old has enjoyed a resurgence at Moore Park since regaining fitness after being plagued by injury in recent years. Zullo played in all but one match as the Sky Blues clinched the domestic double last season and has figured in 12 of the club's 14 games across all competitions this campaign.

The former Australian international could be targeted as a potential replacement for off-contract Spaniard Raul Llorente. Llorente has been a consistent performer for the Wanderers but is yet to receive an offer to extend his stay at Western Sydney, who could be tempted to free up a foreign spot by a potential acquisition of Zullo.

Wanderers declined to comment when contacted by Fairfax Media but it's understood new Wanderers coach Josep Gombau has already begun identifying potential squad changes for next season to coincide with a significant change in playing style from his predecessor, Tony Popovic.

As of December 1, the Sydney FC trio became eligible to speak with rival clubs about a potential move as a free agent for next season. Under A-League regulations, clubs wishing to speak to players from rival clubs must submit written notice to their employers but the timing of the Wanderers' letter to Sydney FC bemused some officials.

However, Sydney FC are understood to be confident Wilkinson, Buijs and Zullo will resist the temptation to move west to join their rivals. Sources informed Fairfax Media the club is confident of retaining all three who are set to be offered contracts for next season. Twenty-eight year-old Buijs is understood to have already entered preliminary talks to extend his stay at the club, while Wilkinson has a clause in his existing contract that will trigger an automatic renewal for another season.

Meanwhile, Sydney FC marquee Milos Ninkovic remains in doubt to play against the Wanderers at ANZ Stadium on Saturday night as he is yet to resume full training with the rest of the team. The Serbian playmaker is coming back from a calf injury and spent much of Thursday's session undergoing fitness tests while taking part in some ball-work and possession drills with the squad.