During his professional career, young Glas wore the jersey of Sixt and Koper Primorska, Serbian Dynamic, Partizan and Mornar. He showed his best performances in the Dynamic jersey, where he scored 18.1 points, 4.2 rebounds and 2.9 assists per faceoff in the 2020/21 season. Glas has always been a part of Slovenia’s national teams of younger age categories, and in 2021 he showed his best performances at the Challenger for national teams under the age of 20, where he averaged 18.4 points, 5.0 rebounds and 2.6 assists per game.

Glas started the 2022/23 season in Partizan Belgrade, signed a contract with Cedevita Olimpija in early January 2023, and was then loaned to Montenegrin Mornar from Bar, where he also finished the season. He averaged 10.3 points, 2.2 rebounds and 2.5 assists per game in the 2022/23 AdmiralBet ABA League. Gregor also excelled in the 2023 World Cup qualifiers, averaging 10.0 points, 1.8 rebounds and 0.2 assists per game in five games.