Montgomery’s versatility on the left was a big selling point for Glass, capable of playing as a full-back or winger.
With Jack MacKenie coming off the bench to make his first appearance since November against the Staggies it allowed Jonny Hayes to move from left-back into an attacking.
The Dons boss reckons he now has strong depth on the left side with Matty Kennedy another option in attack.
“He adds real competition because he can play in multiple positions,” Glass said. “He has obvious qualities.
“It is an important one because Jack has not started a game since Dundee United away in November. Before that it was mid-October so it has been a long time since Jack has been on a pitch for us.
"We need to make sure we have cover for Jack and there will be times when Jack is cover for Adam and Jonny.
“There are three players, plus Matty Kennedy, vying for that one position. There are a lot of players who are capable of playing in that position and it is important that competition is there. “
"If we didn’t add Adam then it might have been too comfortable for some. They need to know they need to work hard to get in the team.”