With the emergence of 21-year-old Tongan international hooker Manase Fainu and a need to find room in their salary cap to re-sign Origin stars Jake and Tom Trbojevic, Koroisau has found himself as the club's sacrificial lamb despite being contracted with the club until 2021.
The Warriors haven't had much go their way in the player market this year. The club was linked with moves for Parramatta half Dylan Brown and Brisbane Broncos duo Matt Lodge and Jake Turpin, but all three players re-signed with their current clubs.
While negotiations go on, Koroisau will front for Manly against the Warriors at Mt Smart Stadium, taking his usual place in the No 9 jersey.
It what is a season defining game for the Warriors as they cling to slim playoff hopes, Hasler noted the fixture was just as important for his Manly side who are peaking at the right time of the year.
"It's still fairly tight and congested, and the only way to resolve it is to win this game and keep knocking the games off as we go. You control your own destiny then."
When the sides met in Christchurch earlier in the year, Manly flew out to a 46-12 win as Tom Trbojevic and Martin Taupau ran riot over the Kiwi side. The club has been playing at a consistently high level in recent weeks, notching up wins over the competition leading Melbourne Storm, Parramatta Eels and Newcastle Knights.
The Warriors have lost two on the bounce after a slim win over the Cronulla Sharks and come into the match off a particularly disappointing performance against the Canberra Raiders.
Despite getting the better of the Warriors last time out and having an impressive record in Auckland, Hasler wasn't reading too much into past results.
"Each game is an entity in its own," he said. "The circumstances change, don't they? So it's about winning it."
