He racked up 113 appearances during his first stint with the club, playing a key role in Glasgow's march to the 2015 Guinness PRO12 title in Belfast.
The Ayrshire native joined the Bulls ahead of the inaugural FOSROC Super6 season, following a spell with London Irish.
Reid will remain an Ayrshire Bulls player, but will train with Dave Rennie's squad and provide valuable cover at loosehead prop for the remainder of the Guinness PRO14 and Heineken Champions Cup campaigns.
Gordon played with East Kilbride before joining Ayr. He has represented Scotland at U18, U19, U20 level and full international level and also played for the club international team.
He was Premier One's player of the year in season 2009/2010.