The other change in the pack sees Nathan McBeth replace the injured Jamie Bhatti at loosehead, while the back row remains unchanged from the side that defeated Cardiff last Friday at Scotstoun.
Smith said: “Ulster are a quality team who will be desperate to make it into the playoffs and to continue their run of form ahead of the Challenge Cup final next week. We are pleased to welcome Gregor back into our matchday squad this weekend. He has worked hard with our medical and S&C teams to put himself in the best position possible, and he is eager to get back onto the field. We know that a strong challenge awaits us in Belfast tomorrow night, and it is a challenge we look forward to facing.”
Glasgow Warriors (v Ulster @ Affidea Stadium on Friday @ 7.45pm kick-off): J McKay, K Steyn, S McDowall, S Tuipulotu, K Rowe; D Lancaster, G Horne; N McBeth, J Matthews, Z Fagerson, G Brown, A Samuel, A Miller, M Fagerson, M Duncan. Replacements: G Hiddleston, R Sutherland, S Talakai, J Oguntibeju, E Ferrie, S Vailanu, B Afshar, O Smith.
Unavailable for selection: Jamie Bhatti (knee), Ryan Burke (knee), Alex Craig (foot), Scott Cummings (calf), Rory Darge (ribs), Jamie Dobie (shoulder), Angus Fraser (back), Adam Hastings (suspension), Huw Jones (foot), Charlie Savala (knee), Grant Stewart (neck), Tavi Tuipulotu (knee), Max Williamson (knee).