Nanai comes off contract at the end of the 2027 season, so he can negotiate with rival clubs from November 1, unless he re-signs beforehand.
On Friday, Payten conceded it was unlikely the Queensland representative would put pen to paper on a new Cowboys deal before the cut-off date.
It sets up an off-season showdown, with the 23-year-old one of the NRL's top second-rowers without a contract for 2028.
Nanai has had an injury-riddled season but remains pivotal to a North Queensland side that are farewelling back-row option John Bateman at season's end and may also lose Kai O'Donnell to the Super League.
At his peak, Nanai has been one of the league's most gifted attacking back-rowers, with a potent running game and ability to compete in the air.
"He's super important ... We know how good a team he makes us when he's on the park," Payten said.
"We want to keep him ... I'd love it to happen before November 1, but I just understand how the game works and how his manager works. So ... I know it won't happen."
Payten's comments come ahead of the Cowboys' final home game against Canberra, who have been attempting to fend off the cashed-up Chiefs' advances towards Hudson Young.
Young's contract saga has dominated NRL headlines this week as head office weighed in following offers from both the Raiders and the competition's 19th franchise.
The NRL will not register contracts deemed below a player's market value and ruled the Chiefs' offer of around $900,000-a-year was below par for Young, who has been offered $1.1 million a season by Canberra.
Sidelined with an Achilles injury, Young is expected to put contract talks on hold until after the season, with Nanai shaping as a potential replacement option if the Chiefs miss their man.
The Raiders clash looms as a chance for the eighth-placed Cowboys to tune up before an elimination final on the road next weekend.
Payten opted against resting Tom Dearden despite a season of injuries, saying the star half needed to find some rhythm after playing just his second game since round 10 last week.
Canberra are looking to end Josh Papali'i's glittering NRL career on a high, with coach Ricky Stuart parachuting Coby Black into the halfback jersey.
Malachi Smith is also set to make his NRL debut from the bench.
"It's a good opportunity to take their performances into the off-season and see where we can keep improving and developing those guys," Stuart said.
"He (Black) has got a big job. Ethan Sanders this year has done an amazing job ... Ethan didn't want to sit out, but he understood the situation."
13°C