Reigning Coleman medallist Hogan broke his thumb after accidentally jamming it in a door, while off-season recruit Stringer has been sidelined with a low-grade hamstring strain.
The duo are expected to miss at least two weeks, though Hogan could miss up to three.
It is a major blow to the Giants ahead of their Sunday clash against Collingwood at Engie Stadium, already without star midfielder Tom Green (calf).
The Magpies are dealing with an injury concern of their own, with star Jordan De Goey ruled out of facing the Giants due to knee bruising.
Even though he has been training fully for the last three weeks, the Collingwood premiership hero suffered a setback during the pre-season and has not progressed enough to be considered for selection.
The Magpies remain hopeful De Goey could be available for their second match of the season against Port Adelaide on March 15.
Stringer, who already has a sordid history of soft-tissue injuries, had complained of hamstring tightness in a VFL practice match on Saturday, leaving the field after one quarter.
Hogan broke his thumb after their final pre-season hit-out against Carlton.
GWS coach Adam Kingsley was already mulling the make up of his squad after the departures of mainstays Harry Perryman, Isaac Cumming and James Peatling.
Jake Riccardi, Harvey Thomas, Toby McMullin and Joe Fonti will also have to serve two-match bans for their involvement in a post-season function last year, with fringe Giants player Josh Fahey out for four.
The Giants will at least welcome back forward Callum Brown from a hamstring injury, while ruckman Kieren Briggs has overcome illness and is available for selection.
"My body is feeling good," Briggs said on Tuesday.
"I managed to get a big block of pre-season in and I'm firing and ready to go."
Phoenix Gothard, looking to make his AFL debut, is a test for the Collingwood clash after spraining his ankle in pre-season.
Green is pushing for a return to round one after originally being slated to return after the club's round-two bye.
Meanwhile, star Sydney ruckman Brodie Grundy is under an injury cloud ahead of the Swans' clash with Hawthorn at the SCG on Friday night.
Grundy suffered a knock to his knee at training last week, forcing him to miss the practice match against Gold Coast.
In that same match against the Suns, star midfielder Errol Gulden fractured his ankle in a major blow.
Gulden had surgery in Brisbane on Sunday with the Swans on Tuesday confirming he will be in a cast for two weeks.
He will meet with his surgeon again in five weeks when the Swans will give an update on his progress.
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