Cornerback Chris Houston, nursing an ankle injury, and safety Louis Delmas, rehabbing an injured knee, were both listed as doubtful in the team's injury report on Friday. Bill Bentley, another corner, has already been ruled out for Sunday with a concussion.
Wide receiver Calvin Johnson was a full participant in Thursday and Friday's practices, and is expected to play despite a foot injury.
Detroit was able to sneak by the St. Louis Rams in their season-opener, 27-23, thanks to a late drive orchestrated by quarterback Matthew Stafford, but with San Francisco's receiving corps of Randy Moss, Mario Manningham and Michael Crabtree for quarterback Alex Smith to distribute to, reliable secondary play could be that much more vital to the Lions' success.
Stay with this StoryStream for full coverage leading up to Detroit's showdown with San Francisco. For more on the Lions, check out Pride Of Detroit. For more on the 49ers, please make sure to visit Niners Nation.