The head coach has picked Glasgow Hawks' backrower for just his second Warriors start against Zebre tonight - his first also came against the Italians in the away PRO12 game earlier in the season. The teenager is at No 8 for this game after playing at 7 for Scotland U20s, and it is still not certain what his best position will be.
Older brother Zander has established himself in Glasgow and Scotland's front-row over the last couple of seasons, and Gregor thinks the younger Fagerson has the potential to match that progress.
Speaking in the Evening Times, Gregor said: "He's a player with real potential. He played very well for the U20s this year at 7, but he did a lot of ball-carrying. He's someone we have high hopes for in the future.
"He's 18. Just now he's an excellent ball-carrier and to have that at 7 is a bonus. If he grows more he could develop into someone who could play No 8 at the highest level.
"We believe any player coming into our system can play for Scotland, but he's obviously playing at professional level as an 18-year-old and he's playing very well for the 20s. So if he carries on working hard he can obviously achieve a lot in the game. He has a great role model in his brother."