It's not every day South Sydney players check their group chat and discover someone on it has been married in secret.

"I just thought we'd get invited," prop Tevita Tatola said, his face splitting into a wide grin.

The happy couple - former Souths star Jai Arrow and his partner Berina Colakovic - on Tuesday announced they had tied the knot in secret, only months after Arrow retired from the NRL with a devastating diagnosis of motor neuron disease (MND).

The 30-year-old's health battle has shocked the NRL, but amid the difficult times, Souths players were pleased to see their former teammate smiling on Tuesday.

"He looked really happy, and yeah, it's just awesome news, the team was really happy for him," Tatola said.

The eighth-placed Rabbitohs face fourth-placed Newcastle on Sunday in a litmus test of their top-eight credentials.

The match also happens to fall on Arrow's 31st birthday.

The NRL is planning to throw what they've billed as the "world's biggest birthday party" for Arrow, complete with a world record attempt for most party hats.

The game will also feature a halftime performance from the Wiggles, a giant birthday cake and the unveiling of four new mascots, along with sponsor donations for every try scored during the game and throughout the month - dubbed "Jai July".

"There's no one more deserving", Rabbitohs centre Jack Wighton said on Tuesday.

Players from all teams are being urged to pull a bow-and-arrow celebration on the try line to honour Jai's fight against MND.

Wighton said the respect had spread far beyond first-grade footy.

"Over the weekend there's been kids, videos doing arrow for him from five years old ... even in my son's game for the weekend", Wighton said

"Seeing everybody get behind it ... just shows what the footy community is about."

At NRL level, the vast majority of round 18 try-scorers celebrated by saluting Arrow.

"Sunday arvo game, it'll be a cracker day, and hopefully we can get a lot of people out there to celebrate Jai's birthday", Tatola said.

Souths' last meeting with Newcastle was a high-scoring blockbuster away from home, with the Rabbitohs clawing back from 28-10 down at halftime to fall short by an agonising four points.

They enter Sunday's rematch with yawning holes in their backline; Cody Walker is suspended for kicking Jack Cogger and Alex Johnston and Latrell Mitchell are still nursing calf injuries.

Mitchell in particular had helped keep the Rabbitohs hanging on by their fingertips in the previous clash against the Knights.

Wighton said the Rabbitohs needed to approach the round-19 clash the "same as every other week without him."

"Everyone's got to do their job ... we've got to try and do our best until the big collars (are) back, and that's what we will keep doing," he said."