In-form Jake Wardle and ex-England international Leroy Cudjoe have both lost their bid to be fit in time.
Although neither injury is expected to keep them out for long, it is a setback for Ian Watson’s side who are still yet to win in Super League and are already missing former Melbourne Storm centre Ricky Leutele.
Giants fought back from 18-0 down to take the lead at Hull KR last week - only to then lose 25-24 following Jordan Abdull’s 77th minute drop goal.
Watson had named the same 21-man squad for the visit of unbeaten Saints but revealed he cannot field the same 17.
“We can’t - I’d love to - but we have a few injuries in there and we named them just to give them every chance to be able to play,” he said.
“Jake Wardle will be out and Leroy Cudjoe. There'll be changes on the back of that as well, to be fair.
“Leroy was 50/50 for this week. We needed to wait for a scan result on Jake and he’s probably going to be a couple of weeks.
“We’re hoping not longer than that. Jake’s had an up and down pre-season, with a few little niggles on the back of what he picked up last year.
“So, to pick this up when he’s come back now is a little bit of a blow to him, especially as he was starting to find his feet and he’d been in the England training squad as well.
"Hopefully he won’t be out long. And, fingers crossed, Ricky may be back next week.”
Sam Wood, who has been playing on the wing, will switch to centre, with Darnell McIntosh likely to move from No1 to the flank.
Giants loose forward Josh Jones won the 2014 Grand Final at centre with St Helens so he could switch to the three-quarters while Australian second-row Chris McQueen also offers similar versatility.
Watson confirmed Lee Gaskell will start at full-back after coming on and making such an impression there at Rovers.
Props James Gavet, Oliver Wilson and Ronan Michael along with winger Louis Senior are the players looking to come into the 17.
Watson, whose solitary win has come in Challenge Cup at Leigh, said: “We've not had our full squad yet for a game.
“We’d like to get a full strength team and really see what we can do as a group.
“But we have got to be patient and make sure we get the boys back fit and healthy so when they get back, they stay back.
“(Losing) two centres doesn’t help but young Sam Wood will move into the centres for us. He’s played centre plenty of times before so he knows it.
“I know he’s still quite young as well but it’s a great experience for him to go up against St Helens and people like Kevin Naiqama and Mark Percival.”
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