NRL club Melbourne have not ruled out another high-profile departure at the end of 2010 after losing Dallas Johnson to an offer the Test lock says was "too good to refuse".

Johnson has been granted an early release from his Storm contract to join French-based Super League club Catalans Dragons on a three-year deal.

Melbourne reluctantly agreed to free the Test and Queensland State of Origin lock.

And Storm chief executive Brian Waldron admitted NRL salary cap constraints meant "once-in-a-career" financial opportunities like that offered to Johnson could mean similar situations arose in future seasons.

"We've always said with our players if they get opportunities overseas which would put them in a better position financially long-term that we would look favourably upon it," Waldron told AAP.

"It's very disappointing from a team perspective, but it's totally acceptable and understandable ... it's not the first and it probably won't be the last unfortunately.

"We know there'll probably be another Dallas-type situation in a year or two - we accept that's part of life."

The Storm have been able to work miracles to re-sign most of their stars and keep them happy under the NRL salary cap.

Greg Inglis, Billy Slater, Cameron Smith and Cooper Cronk are all currently locked away on long-term deals.

Waldron said despite freeing up salary cap space with Johnson's departure, the club would not attempt any short-term like-for-like replacement, preferring to look to youth to plug the gap.

Johnson was a key player in the Storm's two most recent premiership wins, and said leaving was the toughest decision of his career.

"I made my debut in Storm colours, represented Queensland and Australia while playing for them, and have made some life-long friends," Johnson said.

"Storm members and supporters are the most devoted in rugby league and I want them to know that I am indebted for the support they have shown me throughout my career.

"But there are other areas of life I want to explore and living abroad and travelling is absolutely up there on the list.

"The opportunity to continue my rugby league career with the security of a long-term deal and in such a beautiful part of the world was one that I couldn't refuse."

Melbourne coach Craig Bellamy described Johnson as the toughest rugby league player he had seen.

"For a guy his size, to do what he does on the field week after week is simply incredible," said Bellamy.

"He's the toughest player I have ever seen ... he will be missed by all."

Johnson's move looks certain to clear the way for fellow Australian Jason Ryles to leave Catalans Dragons and return home.

Ryles is likely to announce a deal to join the Sydney Roosters in the next few days.

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