Kerr underwent surgery on his knee during the off-season, while Naitanui had a groin issue addressed after rest failed to heal the problem.
West Coast initially hoped the pair would be a chance to feature in Saturday's western derby clash with Fremantle.
But on the club's updated injury list, the pair are listed as being up to four weeks away from resuming playing duties.
Wingman Matt Rosa has already been ruled outfor the next 6-8 weeks due to surgery on his quad, while former Magpie Sharrod Wellington is 4-6 weeks off playing after injuring his ankle in a trampoline accident.
Forward Mark Nicoski, who hasn't played since tearing his hamstring last year, has been placed on the club's long-term injury list after experiencing several hiccups in his rehab.
West Coast enter the season as one of the premiership favourites, but its injury woes will severely test its depth early.
After taking on Fremantle on Saturday, West Coast have a week off, before confronting Hawthorn (home), Melbourne (away) and Carlton (home).
Although the Eagles have plenty of midfield options to cover Kerr's absence, the unavailability of Naitanui will be more keenly felt.
Naitanui earned his maiden All-Australian honours last season, and worked beautifully in tandem with Dean Cox in the ruck.
Cox has the ability to play as the team's sole ruckman, but the Eagles may opt to include either 20-year-old Scott Lycett or rookie Callum Sinclair in order to ease the load on Cox.