It's understood NRL auditor Richard Gardham has final discretion to determine market value using a list of comparative players to reach his decision.

Already this summer Mitchell has been offered wildly different contract sums including more than $1 million per season from the Wests Tigers and a withdrawn contract from the Roosters worth $800,000 per year.

South Sydney's $400,000, one-year deal makes Gardham's determination even more important, given NRL's salary cap laws state a player cannot be registered on a contract worth considerably less than his market value.

However, the sum of the Souths deal could be boosted if the Roosters agree to pay part of his contract for this season.

The 22-year-old Kangaroos and State of Origin representative is considered one of the best in the game, and his value will be determined in similar company, such as James Tedesco, Roger Tuivasa-Sheck and Tom Trbojevic.

All three are on considerably higher salaries.

It's believed Souths' cut-price sum is due to limited space in the salary cap as their priority was to bring Queensland forward Jai Arrow to the club in 2020.

However, it could all change given Monday's confirmation of Arrow's arrival at Redfern in 2021, with Gold Coast reluctant to let their State of Origin star go for the upcoming season.

This could free up space in Souths' salary cap to sign Mitchell on a more substantial contract in 2020, allowing time for the club to offload another player to make room for him in 2021.

It's been reported both Alex Johnston and Dane Gagai could be offloaded to another NRL club.

As the rest of his premiership teammates returned to training on Monday, Mitchell remained with his family on NSW's north coast after being granted a leave of absence from club duties.

Although he is contracted to the Roosters for 2020, it's believed he has played his last game for the club.

However, the longer the situation drags on, the more money the Roosters will pay Mitchell unnecessarily while he is on leave.

Australian Associated Press