Ronny Deila has displayed his faith in youth during his first season as Celtic manager.
Tierney came off the substitutes' bench to make his debut in Celtic's 2-1 win on Wednesday, and Frail believes that showing will serve as motivation to other up and coming stars in the Bhoys’ youth-ranks.
“It’s fantastic when you can sit back and see someone like Kieran coming through," Frail said. "I’m lucky enough to work with him at the final stage before he goes into the first-team, but there has been a lot of work with the coaches with Kieran, and it’s testament to the work that goes in throughout the Academy.
“It gives everyone a lift that the manager will play them if deems them to be good enough.”
Frail has previously hinted that Deila is always looking at including players from the development squad and the hope is that more will be able to follow in Tierney's footsteps.
The left-back has been a stand out performer at under-21 level all season and his recent opportunity has been well earned.
It also provides the youngsters at Celtic with a clear pathway to the first-team, and that could be crucial in the years ahead.
The Bhoys currently have an exciting crop of youngsters threatening to break through and it is important for their development that they have a manager with as much faith in youth as Deila.
The Norwegian boss has already given the likes of Tierney, Callum McGregor and Liam Henderson fairly regular action this campaign and it would not be at all surprising to see some more of the club's youngsters called upon before the season finishes.