The 24-year-old centre-back, who is on a season-long loan from Celtic, has taken the place of Norwich defender Andrew Omobamidele, who has been ruled out after suffering a groin injury his his club’s 1-1 Sky Bet Championship draw with West Brom at the weekend.
Scales received his first call-up for the Ireland squad in September last year in similar circumstances as a late injury replacement but he has yet to be capped at senior level having made six appearances for the Under-21s.
He was red carded at the weekend after picking up a second booking for bringing down Hibs counterpart Ryan Porteous in the box for a controversial penalty which resulted in Aberdeen relinquishing their one-goal lead and going on to lose the match 3-1.
A Football Association of Ireland statement said: “Norwich City defender Andrew Omobamidele has been ruled out of the Scotland and Armenia matches.
“The 20-year old defender sustained a groin injury in the 1-1 draw against West Bromwich Albion and has been replaced in the squad by Aberdeen defender Liam Scales.
“Scales reported for duty this morning ahead of the squad’s first training session in Dublin as preparations begin for the two UEFA Nations League fixtures against Scotland and Armenia.”
Ireland claimed a 3-0 win over Scotland in Dublin in June and will travel to Hampden Park on Saturday for the reverse fixture before hosting Armenia next Tuesday.