The 20-year-old has been a revelation for Celtic so far.
The 20-year-old striker has been a revelation in Glasgow following the bargain-busting £500,000 move from Fulham in the summer.
The French hitman has netted 11 goals in all competitions for the Bhoys so far and he will look to add to his haul on Wednesday when Celtic host Borussia Monchengladbach in the Champions League.
He has already proven himself a lethal striker not only in Scottish football but in general, following his brace in the 3-3 draw with Manchester City last month.
Those two goals simply reiterated what Celtic fans already knew about him after Dembele netted a hat-trick in the 5-1 demolition of Rangers, and Armstrong says the youngster is a great asset.
“Every single big game that he has played in, he has produced,” he told The GET. “He is big, he is strong, he is fast but he is also very technical too and he is a great asset to have.
"His performance in the Champions League against Manchester City and in the Rangers game earlier on were just phenomenal."