Glenn, the Bills' left tackle, suffered an ankle injury in the third quarter of this past Sunday's 52-28 loss to the New England Patriots and did not return.
Urbik, the starting right guard, also sustained an injury to his right foot/ankle area. The four-year veteran left the contest in the second quarter and confirmed to the Bills' official web site that he has a high ankle sprain.
"I've got to take it day by day," Urbik told the site. "You can't help a guy falling on your leg. It's unfortunate that it's happened two of the last three years. So I'll be out this week and we'll see where it goes from there."
Both Glenn, a rookie, and Urbik have started all four of Buffalo's games this season. The Bills (2-2) will face a Niners defense that currently ranks fourth in the NFL in opponents' scoring and total yardage.