With the Perth Bears set to join the competition next year and the PNG Chiefs in 2028, talk has turned to when and where the game is best suited to move to a 20-team league.
Cleary knows the New Zealand market better than most, having played in the Warriors' first grand final in 2002 and coaching them to their second in 2011.
The Kiwi side has yet to win a competition but there is a fair argument that in 2026 under Cleary protege Andrew Webster, the Warriors shape as Penrith's closest challengers.
But Cleary, who has also worked as an assistant coach with the New Zealand national team, is concerned a second side in the country could negatively impact the Warriors.
"I've got to be careful what I say here, with all my friends in New Zealand - I definitely think we need to make sure the Warriors continue to get the support they need," Cleary said.
"They're definitely a club on the rise and that's been a long time coming.
"I think it's really important that the game needs to foster that (and) be careful to (not) split that."
Talk of expansion in New Zealand comes at a time when the Warriors have enjoyed regular sellout crowds in the years since the COVID-19 pandemic.
The construction of Te Kaha stadium in Christchurch, which hosted the Warriors' 38-20 win over North Queensland last Sunday, has meant the NRL could start a side in the South Island without having to invest in infrastructure.
"How good was that stadium?" Cleary said.
"There are a lot of good players coming out of Christchurch, I know that, and there's more and more the Warriors are getting from down there.
"It's definitely good signs. I don't even know when the 20th team's coming in, so it could be the right time, I don't know."
