Latrell Mitchell has put South Sydney's rivalry with the Sydney Roosters aside to throw his support behind Angus Crichton as he seeks treatment for mental illness.

The Roosters second-rower was last week diagnosed with bipolar disorder, with his club contemplating applying for salary cap relief.

The forward has taken an indefinite break from the sport and Mitchell, who played in last year's World Cup final win with Crichton, said he was proud he put their clubs' rivalry aside to offer his support to the 27-year-old.

"I reached out to his dad to make sure they are going alright," Mitchell said.

"That's the type of person I am, I try to reach out and put my best foot forward.

"I've got a good connection with his old man, Charlie.

"Gus, we won a comp together, I wanted to make sure he was alright and they are travelling OK.

"It is what it is. I don't want to comment too much on it, it's their personal lives, with what they are going through.

"Obviously the media has to leave it alone now and let him just heal, do what he needs to do."

Crichton's ongoing absence has led to the Roosters weighing up a move to get the value of his salary taken off the club's cap.

The NRL say no official application has been made, although one would be considered on its merits.

Currently the NRL only provides salary cap relief due to unavailability as a result of medical retirements, injuries sustained on representative duty or a player being subject to the no-fault stand-down policy.

Meanwhile, the Roosters announced on Wednesday that they had extended the contracts of forwards Victor Radley and Egan Butcher until 2027 and 2025 respectively.

"Victor and Egan are hard workers who love the tough stuff," said Roosters coach Trent Robinson ahead of Sunday's NRL season opener against the Dolphins.

"They're also good men who play an important role within our squad so it's great to have them locked in to the club's long-term plans."