Gregan felt he would be better prepared for the World Cup if he shied away from the physical demands of playing eight matches, including four Tests, throughout the tour.
The Wallabies take on Wales, Italy, Ireland and Scotland in Tests during November, as well as A sides from Ireland and Scotland.
"I haven't completed a solid block of physical training since 2000, so having the opportunity to rest from the Spring Tour will give me a chance to make some good physical gains leading into a World Cup year," Gregan said.
Last year, vice-captain Stirling Mortlock chose not to take part in Australia's disastrous Spring Tour, which saw them win only one Test from four starts, instead staying at home to undertake an extended training regime.
The decision proved a good one, as Mortlock impressed during the opening rounds of the inaugural Super 14 season, and Gregan hoped the same move would pay dividends for him.
"If you look at Stirling, he definitely had one of his best years this year after getting a full pre-season of training prior to the Super 14," said Gregan.
"Having that chance to complete two months of physical training is very rare these days and it really rejuvenated Stirling's career."
Wallabies coach John Connolly quickly ended speculation that Gregan would not play again, but added that his place in the World Cup team was no certainty, particularly if young scrumhalf Josh Holmes impresses.
"This does not mean that George's Test career is over," said Connolly.
"We understand from George's perspective that he wants to go out on a high after the World Cup and is focused on getting into the best possible shape to give himself the chance to perform at his best next year.
"I think he's had a very solid year for the Wallabies and has led the team pretty well.
"Having said that, no one is guaranteed a place in the team (for next year). The tour will be important for a number of players, as will next year's Super 14."