Victory will be without Daniel Georgievski, Connor Pain, Kosta Barbarouses and Jason Geria for the crunch match at Allianz Stadium, with all four players away on international duty,
Scott Galloway is likely to be available after being unable to travel with the Olyroos to China, but Mark Milligan, who was forced to pull out of the Socceroos squad for the friendly away to Japan next Tuesday due to a knee problem, may not recover in time to tackle the Sky Blues.
Several more players were absent from training on Wednesday as they underwent recovery work behind closed doors, while veteran Archie Thompson finished the session early.
Unless the situation improves, Kevin Muscat may well have trouble putting together a competitive XI this weekend, but Leijer backed the team to demonstrate their strength-in-depth once again.
"It's not ideal but Musky's put together a really good squad," he said.
"I'm sure we can still put out a very strong team."
The former captain revealed his fellow Victory stalwart Thompson has been dealing with a niggling injury but backed the forward to come good by Saturday.
"He's had something going on there for a while but he's been managing it quite well," Leijer said.
The clash with Sydney is likely to arrive too soon for Nick Ansell to feature, despite the young centre-back closing in on a return to full fitness.
"Nick, they have to be careful with him," Leijer said when asked if the 20-year-old might be rushed back.
"He's had quite a serious injury, he's managed it really well. He's been great off the pitch, training hard and looking after himself. The medical staff will do the right thing by him."
Wednesday's training session was heavily delayed as the squad underwent an extension video review of their opponents, with Leijer confirming the Big V will be doing plenty of homework on a team who are joint second and unbeaten so far in 2014-15.
"We will do a lot of work on Sydney," he said,
"Tomorrow's our big preview towards the weekend. They've been good this year, Arnie (Graham Arnold's) really got them well disciplined, well structured - they're going to be hard to beat."
Finally, having missed the 2-0 win over Wellington Phoenix after being sent off for a picking up a second yellow card for dissent away to Perth Glory in the Westfield FFA Cup quarter-finals, Leijer announced a new tactic in his bid to avoid more unnecessary suspensions.
"I've decided not to speak to referees at all. That's something I'm going to work at."