Glenn, who had been sidelined since June minicamp with an undisclosed condition, was limited in Saturday's practice and won't immediately receive a full workload.
"We're going to take it very, very slowly to see how he comes back in the first couple days," coach Doug Marrone said. "We will just do a little bit on the side and a little bit individual. You won't see him participating in any team [drills] for a while. Then we'll see how he responds because I really don't know."
Glenn did not reveal the medical condition that kept him out of practice and the first two preseason games, calling it a personal situation.
Rookie Seantrel Henderson started the first two preseason games in Glenn's place. It's possible that Henderson could now push for a starting job at right tackle, where second-round pick Cyrus Kouandjio has yet to challenge incumbent Erik Pears.
"If Cordy comes back and he's at form, then we'll see what the best combination of five [offensive linemen] is," Marrone said. "Cordy's not back yet and that may be a long time. Seantrel can play left tackle in this league."
Along with center Eric Wood, Glenn was considered a strong point along a Bills offensive line that had question marks at its other three positions last season.
"He looked good out there in individual drills. We're going to take it slow with him, he's had some time off, but we're definitely excited to have him back," Wood said. "Definitely excited to have a caliber player of Cordy Glenn, one of the best left tackles in the league -- in my opinion -- pop him into our lineup."
Glenn, a 2012 second-round pick from Georgia, has started 29 games in his first two seasons.