The 30-year-old forward damaged his hand against today's opponents Nottingham Panthers on December 27 and didn't return until March 24, with just two games of the regular Elite League season left.
He played a starring role for Sheffield in the quarter final win over Guildford Flames, as he did last year in the final against Cardiff Devils, when he scored and assisted and generally orchestrated some of Sheffield's best moves.
He can be the difference, today, if he hits peak form, against Panthers.
"Yes, that's right" says Steelers coach Paul Thompson, responding to the suggestion that Armstrong can be their match-winner this evening.
"When he's on, he is unplayable.
"I'm not sure we would have qualified if John Armstrong is not in the line up. It's like not winning the league with Joey Martin in your (Cardiff Devils) line up!
"He is a hell of a talent and if we are to win this weekend John and all the boys will have to be on top form."
Steelers face off against Nottingham at 5pm after the Fife Flyers v Cardiff Devils semi final.