The NRL has offered to help Melbourne explore ways to prevent Greg Inglis from switching to rugby union but it will not bend the rules to keep rugby league's best player in the game.

Amid reports Inglis's interest in a code switch is growing and French rugby union clubs are circling, the Storm have asked the NRL to help explore measures to keep Inglis in rugby league.

NRL boss David Gallop confirmed he had held discussions with Storm chief executive Brian Waldron about ways to increase Inglis's earnings but said the league was limited to introducing him to potential sponsors.

Gallop ruled out allowing any salary cap exemptions or offering direct financial assistance despite an alarming trend of the game's elite players, including Sonny Bill Williams and Mark Gasnier, being enticed overseas by big-money offers.

"We're happy to talk to them about potential relationships with our sponsors but we've made it clear there can't be any exceptions to the salary cap rules," Gallop said.

"We're just introducing him to our sponsors, which is really the only measure we can do."

Fears the Kangaroos and Queensland star could jump ship have intensified since he publicly talked about linking up with Anthony Mundine and Khoder Nasser - the management duo who masterminded Williams' defection.

Reports on Friday suggested Inglis has already spoken to his parents about a future move overseas and had received their blessing.

Inglis has two more years on his current deal but Melbourne would struggle to offer him around the $500,000 he is likely to demand when it expires.

It means Inglis's earnings would need to be topped up by a third-party sponsorship deal, similar to that arranged for Gasnier with the Dragons.

"It's something that we regularly do with elite players," Gallop said of overseeing sponsorship arrangements.

"Sometimes there are sponsors willing to get on board with them but it's very important that we don't make an exception to the rules.

"We can't start making exceptions for certain players."

Gallop said the NRL would investigate other ways to encourage top-line talent to remain in Australia but ruled out a centralised contract system similar to that of the ARU or Cricket Australia because it did not work with a salary cap system.

He did, however, hint an increase in representative payments for Test and State of Origin players could be on cards for next season.

"There's potentially an opportunity to do that next year but we need to look at the overall budget before we agree to that," Gallop said.

Meanwhile South Sydney declared their investigation into Sunday's socket throwing incident closed despite being unable to identify the culprit.

Manly centre Steve Matai was the target of the small metal object as he was sent to the sin bin in the Sea Eagles' shock loss at ANZ Stadium.

After a five-day investigation, which included interviews and extensive reviews of CCTV footage, Souths chief executive Shane Richardson said the club had been unable to identify the culprit and he called on any witnesses to provide information.

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