There are five uncapped players in Cheika's 33-man squad but Samu who signed with a two-year deal with the Brumbies this week isn't one of them.
Rugby Australia had submitted an official request to New Zealand Rugby for the release of the Australian born Samu but approval was yet to come through.
While World Rugby's regulations force the release of players for Test duty in June, there is a sub-clause that allows unions to deny such requests when the player holds dual eligibility.
"I have been told at this point I can't select him. But there is a spot for him there," Cheika said.
"At this point, it is in other's hands.
"I am not really involved in that part of it but I am hoping that there will be some more clarity about that (on Thursday)."
While there is still hope Melbourne-born Samu will be cleared in time to take on Ireland, it would be entirely at New Zealand Rugby's discretion.
The 26-year-old is also eligible for the All Blacks through residency.
While World Rugby's regulation nine forces the release of players for Test duty in June, there is a sub-clause that allows them to deny such requests when the player holds dual eligibility.
If Samu isn't made available, Cheika said newcomer Caleb Timu and Lukhan Tui were possible contenders to play at No.6 for the series opener in Brisbane on 9 June.