Ronny Deila wants his stars to keep up their solid form.
Mackay-Steven and Armstrong both joined Celtic in January but have already made a lasting impression at Parkhead.
Such is the success of the young duo that many are calling for the Hoops to be called up to the Scottish national squad.
Before Gordan Strachan puts in any calls, however, Celtic boss Deila has warned that the pair must show consistency over time.
Deila even included a 'wise saying' of England boss Roy Hodgson, urging Mackay-Steven and Armstrong to continually play at their current high level.
“They have shown they can play at a high level but they have to show it consistently over time,” the Bhoys boss told reporters.
“If they do that, we can start talking about them playing in the Scottish national team. It’s like Roy Hodgson said once, you don’t want to be like fireflies who only last for one day. You want stars because they last forever.”
Celtic face second-placed Aberdeen in a huge Scottish Premiership clash later today and, should they go on to win the league - or possibly even the treble - Mackay-Steven and Armstrong will be remembered for their contribution.
That's saying a lot considering how short their stay so far with the Hoops has been. But the energetic duo have certainly made an impression. How soon before a Scotland call-up does beckon?