The 49ers suffered several injuries in their week one match up facing the Vikings, two alone on the offensive line. Losing Mike Person and Joshua Garnett forced the team to use swing tackle Garry Gilliam at right tackle and rookie Mike McGlinchey at right guard. If any other players were injured, the only other option would have been to have a tight end on the line as they only dressed seven offensive linemen.
Having McGlinchey play at guard wasn't the plan but it was a necessity.