CSL clubs will be limited to three foreign players per game for the 2017 season, which begins on March 3, down from five last year.
Kruse and midfielder James Holland moved to Liaoning FC last month, joining James Troisi at the club and international team mates like Matthew Spiranovic (Hangzhou Greentown) and Apostolos Giannou (Guangzhou R&F) in China.
Winger Kruse's need for gametime is particularly acute as he made only three appearances in cup competitions for Bayer Leverkusen this season before his move.
"You hope he has got a move where he plays regularly. There are new rules for him and Giannou just to play," Postecoglou said.
"There are no guarantees any more. That's a bit of a concern."
Australia's campaign to reach a fourth straight World Cup finals reaches the business end this year and the Socceroos are also featuring in the Confederations Cup in Russia.
With the World Cup following in 2018 and Australia's Asian Cup defence the following year, Postecoglou said this would be a crucial year for 28-year-old Kruse, who has played 48 times for his country.
"He is still in the prime of his career," Postecoglou added.
"Robbie, at his best, is more than capable of playing at the highest level. He just hasn't had the opportunity because of injuries and game time," he said.
"This next 12 months are big for him. He will either become a key player and take on that experienced role now, or get bypassed by others. That's his challenge.
"I believe he can be a key player in our team, and he needs to be now."
(Reporting by Nick Mulvenney, editing by Amlan Chakraborty)
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