The former St Helens skipper, now in his second season with Canterbury Bulldogs, said Sam Tomkins' impending move to the southern hemisphere - widely tipped to be with New Zealand Warriors - in 2014, along with move of England forwards Gareth Hock and Lee Mossop to Parramatta, will not end there.
"It is a trend that will probably continue for a couple of years," Graham said on the Peter Sterling show 'Sterlo' on Australia's Fox Sports.
"I suppose it is having an effect on the competition back home. It is a sort of a Catch 22 from an international England point of view.
"You probably want players to come here and play against the best players in the world on a week-to-week basis, testing themselves in the best competition in the world.
"You also need a strong Super League as well. I don't think they have to be mutually exclusive. I think you can have a strong Super League and a strong NRL but I think at the minute the biggest threat to Super League is still rugby union back home."
Graham, who was given a 12-match ban after last season's 14-4 Grand Final loss to Melbourne when he bit the ear of Australia full-back Billy Slater, said he was still trying to come to grips with the week-to-week intensity of the NRL compared to Super League.
"Back home, with all due respect to some of the teams, they are probably not at the standard of the top-end teams," he said.
"Every week (in the NRL) you have to be on your game. There are star players in every team and that's probably not the case back home."
England coach Steve McNamara caught up with Graham and the rest of the Sydney-based England players on Wednesday for a talk about the game against Italy, scheduled as a warm-up friendly before the World Cup.