Ibbotson, who did not play in Fremantle's NAB Cup losses against West Coast and Hawthorn on Sunday, suffered ligament damage after incurring a "high end" ankle injury, football manager Chris Bond said on Monday night.
The club, already hit by injuries to promising midfielder Anthony Morabito (knee) and Roger Hayden (foot) this pre-season, released a statement saying it expects Ibbotson to miss six to eight weeks.
The injury could thwart the 22-year-old's ambitions of spending more time in the midfield this season after a summer aimed at preparing him physically for an on-ball role.
The versatile Ibbotson, who has been elevated into Fremantle's leadership group for 2011, played his best football across half-back last season, but Fremantle coaches directed him to develop as an inside midfielder during his end of season review.
He will now miss a crucial period leading into the season, with Fremantle's round-one clash against the Brisbane Lions at the Gabba less than six weeks away.
As well as Morabito, who has been ruled out for the year after undergoing a knee reconstruction, and Hayden, who is expected to miss half the season, Fremantle has suffered a string of minor injuries.
Hayden Ballantyne (foot), Matt de Boer (hamstring) and Joel Houghton (arm) have had interrupted preparations, while Michael Barlow (broken leg) and Tim Ruffles (knee) continue their rehabilitation.
Fremantle leaves on Tuesday for a three-day community camp in Kalgoorlie, with a select group of players - including star midfielder Stephen Hill - left behind to continue training.
