The Canadian centreman had been topping the points charts’ for Sheffield Steelers until he damaged his finger in a fight with Nottingham Panthers’ opponent Mathieu Brisebois.
Armstrong had an operation two weeks ago to repair a tendon in his finger and was told it would take 12 weeks to heal.
That takes him through to the end of March, when the regular EIHL season finishes and the Play Offs begin.
The forward, who turns 30 next month, recalled the fight behind the goal at the NIC saying the injury happened: “At some point during the fight when I was holding on to his jersey.
“It didn’t hurt immediately afterward, but I knew something was wrong because my finger wouldn’t bend at all.
“The tendon had to be reattached within two weeks of the injury. If not, the surgery is more complicated and the recovery is significantly longer.”
Armstrong (who had amassed 35 points in 37 games and was having his best season for Steelers) was gutted to lose out on taking part in the club’s prestige European tournament in Belarus.
“It’s disappointing to lose momentum and it would’ve been great to represent the UK in the Continental Cup last week” he said.
“I am incredibly frustrated that a finger injury is keeping me out of the game for so long.
“Last season, even though I had some injuries including a broken bone in my hand, I was able to play every game and was hoping I could do the same this season.
“Unfortunately, this is an injury that needed to be repaired right away.”
Armstrong is keeping in shape by working on lower body strength, in the gym, with strength and conditioning coach Danny Mawer.
“I am also completing my final year of study at the University of Sheffield, which is keeping me pretty busy especially since I have to type my papers with one hand” he said.