Wilkinson was admitted to hospital in Tokyo during Newcastle's recent pre-season tour to Japan suffering from an inflamed appendix, and is now undergoing further tests on his return home.
Although his club boss, Newcastle rugby director Rob Andrew, is hopeful that England World Cup hero Wilkinson won't require surgery, an operation is still possible.
If Wilkinson, whose career since the 2003 World Cup has been blighted by repeated injury setbacks, requires surgery, then he could be out for up to six weeks.
"Jonny is having further tests to see the nature of the inflamed appendix, which is what he has had," said Andrew, at the Guinness Premiership launch in London.
"We are hopeful that it has settled sufficiently to allow him not to have an operation to remove his appendix. That is the position.
"A normal appendix operation would put him out for between four and six weeks.
"It is unlikely at this stage, albeit there is a one in three chance that an inflamed appendix will return within a period of time."
Newcastle, England and Wilkinson are desperate for him to enjoy an injury-free run.
So-called "stinger" injuries to his neck and shoulder, plus two knee injuries, had the combined effect of keeping him out of England action since his drop-goal won the World Cup in Sydney almost two years ago.
England kick off their Autumn international series against Australia on November 12, and Wilkinson showed during the recent British & Irish Lions tour of New Zealand that he needs games under his belt.
While Wilkinson awaits his tests results, another high-profile Premiership player also faces a delayed entry to the new campaign.
Saracens' rugby league recruit, former Great Britain captain Andy Farrell, had hoped to make his union debut in a pre-season friendly against Harlequins on Saturday.
But the toe injury that forced him out of last week's game against Bedford will keep him on the sidelines.
"Andy has been training full-time since June 27. He picked up a toe injury last week, and he is like any player in that if he is not 100 per cent fit, we won't consider him," said Saracens head coach Steve Diamond.
Diamond also confirmed that England flanker Richard Hill faces a battle to play at all this season after sustaining another serious knee injury.
Hill was hurt during the Lions' first Test defeat against the All Blacks in Christchurch, having only recovered a few months previously from another knee problem that hit his season.
"Richard has suffered an horrendous recurrence of a knee injury, so we probably won't see much of him this season," added Diamond.
"If we do see him this season, then it will be in the latter months of two."