The Sky Blues' attacker was hopeful of being ready for Saturday's A-League clash against Wellington but could now be out for another two weeks.

That includes the club's next league game against Adelaide, and he'll be racing the clock to be fit for their first ACL group match on March 6.

"He's probably a setback, maybe another week or two. It's an ongoing thing with him," coach Steve Corica said on Friday.

"We just take each week at a time and and we'll go from there with Siem."

The Sky Blues are due to name their Champions League squad on Monday, with much of the focus on which three of their four foreigners are named.

Key attackers Milos Ninkovic and Adam le Fondre are all but certainties, however de Jong's status could open the door for Jop van der Linden to be included.

Corica conceded wanting to pump minutes into de Jong before hosting Chinese Super League champions Shanghai SIPG at Jubilee Oval.

"He's our marquee, he's been out for quite a while now and we're missing him. So it'd be good to have him back as soon as possible," Corica said.

Van der Linden hasn't been sighted since suffering a hamstring injury against Wellington in mid-December, but had already been falling out of favour.

Despite being available for selection, he has been omitted from the squad to face the Phoenix for the club's "away" game in Campbelltown.

"We need to see how far away Siem is as well with his injury. Obviously we're going to miss taking one over, and it's disappointing for whoever it is," Corica said.

Corica's side have only picked up four from a possible 12 points in their past four games, including a loss to lowly Brisbane and draw with Central Coast.

They are now 10 points behind pacesetters Perth in third spot.

Wellington are sixth with 28 points, just six in front of seventh-placed Newcastle with eight games remaining in the regular season.

STATS THAT MATTER

* This will be the third A-League game at Campbelltown Stadium, and the first there for Sydney FC and Wellington.

* Sydney FC are winless in their past two A-League games. The last time they went this long without a win was an 11-game stretch in 2016.

* Roy Krishna leads the league in touches in the opposition box with 123, while Adam le Fondre leads the league in shots with 35.

Australian Associated Press