The Indonesian Premier League (LPI) is an independent professional league launched last month without recognition from world governing body FIFA or the Football Association of Indonesia (PSSI), which has banned LPI players from representing the national team.
Ishak and Khaizan resigned from their PSSI-supported Indonesia Super League (ISL) team Persib Bandung on Monday but because their prospective new LPI side is not recognised by the Singapore Football Association (FAS) their international careers might be on hold.
"As required by FIFA statutes and regulations, the FAS only recognises leagues that are officially sanctioned by the respective member associations of FIFA," FAS official Isaac Christian told Reuters on Tuesday.
"In this instance, the FAS will be writing to the PSSI to seek further information about this new league.
"We will also seek input from FIFA before any decision is taken."
The 19-team LPI, which includes three sides who switched from the ISL, is the brainchild of oil tycoon Arifin Panigoro. It is aimed at improving the level of the game in the country ranked 129th by FIFA and is backed by the country's sports minister.
The Singapore duo are expected to become the latest names to join the league which has been on a high-profile recruitment drive following the capture of former England international Lee Hendrie last month.
"We will be very glad if they come," LPI official Abi Hasantoso told Reuters.
"They are good players with high-skill football and determination and are key players for the Singapore national team.
"We hope they can improve their new team to compete with other LPI teams. They are big names. Indonesian football lovers know them very well. It sounds great for LPI and Indonesia football."
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