He has also made an emergency appeal to their opponents to see if they will allow on-loan Andre Savielo to play against his parent club.
French prop Gadwin Springer is out with an ankle injury suffered in Friday’s win over Wakefield Trinity while fellow forward Grant Millington is unlikely to play either due to the heart complaint that saw him come off early.
Powell said: “Gadwin’s not great. He’s got a protective boot on at the moment.
“He won’t play Thursday and probably won’t play again this season.
“He’s got a scan this afternoon so we’ll know the full extent then. That’s another tough one.
“We’re just waiting on a specialist report on Millo, too.
“It’s probably extremely doubtful he’ll play at Saints so we’re struggling for numbers in a big way.
“We’ve lost (Lee) Jewitt and (Frankie) Mariano for the season and cancelled training for today.
“We’ve put it back until tomorrow, hopeful that we can get a couple who can train then.
“It’s just down to pure numbers. It is tough. We were down to five in the pack but one of those can’t play (Savelio) so we could nearly play if we put Jake Webster in the middle.
“But Luke Gale wouldn’t have trained today so it was just pointless running the session.
“We’re scared of doing any contact in case we get any more injuries! It will be interesting.”
Explosive prop Savielo has been impressive since joining on loan from Saints in July until the end of the season.
Castleford have won four of the five games in which he has played but, under the terms of the loan, he is not allowed to feature on Thursday.
Powell hopes Saints, who still need points to secure fourth spot, will allow the 21-year-old to play given Tigers’ injury-crisis.
“I’ve asked the question. I’m just waiting for a response now,” said the coach, who could possibly see second-row Mike McMeeken return after missing the last two months with a broken leg.
“He’s done well for us. He had a little bit of an offish game against Warrington but was great again last week.
“I’m disappointed he can’t play for us against St Helens if that remains the case.
“But we knew what the arrangement was so we have no complaints about that.
“I’ve spoken to Keiron (Cunningham) and whatever will be will be; he’s their player so I have no real beef with whatever happens.”
There is speculation Savelio – who has surprisingly fallen out of favour with head coach Cunningham - is being touted around NRL clubs for 2017.
Asked if Castleford would be interested, Powell said: “I’ve not spoke to him or St Helens.
“He’s a St Helens player for next year and I think it’d be disrespectful for us to be talking to him about anything part from what he does for us this year.”