The Giants had been hopeful vice-captain Kelly would make his comeback in the second half of the season after the 31-year-old underwent hip surgery in November.
Kelly had the operation for a recurrent right hip issue, with the club describing the surgery as "unprecedented". It required "some prosthesis components", but not a hip replacement.
With eight home-and-away rounds remaining, Kelly has yet to start running again.
Kelly is just one of 15 injured GWS players, with the 14th-placed Giants (6-9) facing an uphill battle to secure a finals berth.
GWS are on a three-game losing streak, with ladder leaders Fremantle (14-1) out to continue their misery at Manuka Oval on Saturday.
"He's hopefully starting to run next week," Kingsley said of Kelly.
"Starting to run again and playing within a seven-week or eight-week window, whatever, is probably not a window that he's going to be able to get back in.
"This one hasn't come on as quickly as what I would have hoped anyway. That's the nature of what was a pretty significant surgery.
"I certainly knew it was going to be that way."
Kelly was limited to just 15 appearances last season with hip and calf injuries, but played a starring role in a 19-point elimination final loss to Hawthorn.
His injury layoff comes as the Giants face a crossroads in their attempt to keep their premiership season alive.
GWS skipper Toby Greene has yet to re-sign with the club amid speculation the proven match-winner is open to returning to Victoria.
Greene's heir apparent Tom Green is also on the radar of expansion club Tasmania, with the ball-winner - sidelined this season with an ACL injury - contracted until the end of 2027.
Inaugural Giants player Stephen Coniglio's contract also ends this season, while Kelly is tied to the club until 2029.
GWS are also on the search for a new chief executive to replace inaugural boss Dave Matthews.
Amid all the noise, Kingsley is confident Kelly can get back to his best.
"If he can get back physically and he'll have a whole pre-season to be able to do that, then I don't see any reason why he couldn't return to what he's been in the past," Kingsley said.
"But again, there's a lot of water to go under the bridge before that happens."
Key defender Jack Buckley's return from a hamstring issue has also been delayed after initial optimism he would line up against Fremantle.
The Giants have at least found some reprieve, with key foward Max Gruzweski avoiding surgery for a dislocated patella following last week's defeat to Hawthorn.
Gruzweski will miss at least four weeks, while the Giants have yet to ascertain Brent Daniels' timeline from a calf strain.
Kingsley is at least hopeful forward Daniels will return before the season's end, provided the Giants make finals.
"If we manage to do that, then I think he'll be every chance," Kingsley said.
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