Centreman Armstrong suffered a finger injury as he brawled with a Nottingham Panthers player in the previous match.
It's a bad wound and could last much of the rest of season - which may mean Sheffield will have to dip in the market again.
A club spokesman said Armstrong, who has scored four points in his last three matches, could be out "10 to 12 weeks."
His absence meant a change of formation with forward duties for Cole Shudra.
Zack Fitzgerald sat out a one-match ban.
Goaltender Ervins Mustukovs started the game having broken the EIHL shut out record at 241.28 mins, a stretch which covered five games and had seen 86 saves in that time.
Storm without Matt Bissonnette, Ashley Smith and Chris Auger, almost conceded after 11 seconds when Mathieu Roy had a chance.
But the first shift of the Valdix night returned a goal, with Robert Dowd netting after 88 seconds.
Manchester responded well - they had five or six shots on Mustukovs within a short spell and looked mobile for their size on the big ice.
But Scott Aarssen could have added another for Sheffield.
The middle period started as well for the home club as the first did - with the main protaganists involved again.
This time Dowd turned provider, his delicious pass from behind the net was put away first time by Andreas Valdix 59 seconds in.
Storm had barely put a foot wrong, considering they were 2-0 down.
But they could not match the quality of the Valdix line where it mattered most.
Storm threw everything but the kitchen sink at Steelers, hoping to stop Mustukovs' clean sheet.
But Jay Rosehill fanned on a close-in opportunity and Matt Beca pounded a shot off the Latvian's right shouder - the goalie then going on to produce two excellent glove saves.
Sheffield concentrated on closing down the neutral zone and taking shooters away from good areas.
But Mustukovs' steely determination was their major asset.
And the game was put completely beyond Storm when Dowd scored on the Power Play.
After the match coach Paul Thompson said he would be complaining to the League discipline administrators about an attack on Mark Matheson.
He said they were pleased with the result, but would not be getting "too high" about the sequence, with a lot of hockey left to play.
Thompson acknowledged the injury to Armstrong was a sickener, but said the club would be pressing ahead with its aim to bring in reinforcements to the forward line...something they'd had in mind before the injury.
Steelers are third in the table tonight after the victory.
Saturday 30th December
Belfast Giants 4 Braehead Clan 2
Cardiff Devils 6 Milton Keynes Lightning 3
Fife Flyers 5 Guildford Flames 3
Nottingham Panthers 4 Coventry Blaze 3
Sheffield Steelers 3 Manchester Storm 0
Sunday 31st December
Braehead Clan v Dundee Stars - 2.00pm
Edinburgh Capitals v Fife Flyers - 4.00pm
Monday 1st January
Coventry Blaze v Nottingham Panthers - 6.00pm
Manchester Storm v Sheffield Steelers - 5.30pm
Milton Keynes Lightning v Cardiff Devils - 6.00pm
Tuesday 2nd January
Dundee Stars v Braehead Clan - 7.30pm
Guildford Flames v Edinburgh Capitals - 7.30pm
Wednesday 3rd January
Fife Flyers v Manchester Storm - 7.00pm
Challenge Cup Quarter Final 2nd Leg
Nottingham Panthers (1) v Milton Keynes Lightning (2) - 7.30pm