Gregor, the former Caledonia Reds and Edinburgh Reivers forward, is to return to Scottish rugby after five years in Italian club rugby, first with Overmach Parma and then Viadana.
"I've always been impressed with Gregor," Hugh Campbell, Glasgow's head coach, said this afternoon. "He captained the Students' World Cup squad that I coached in Italy five years ago.
"He's a player of tremendous potential, and I know he's desperate to prove himself again in Scottish rugby. We've yet to see the best of him."
Gregor is a product of the Moray club in Elgin, and he subsequently progressed to Dundee High School FP before joining the professional ranks and playing in the Heineken Cup with first Caledonia Reds and then the Reivers. He also played under-18 and under-21 international rugby before leading the Scotland squad in the 2000 Students' World Cup in Italy.