FOXBORO -- The Patriots may be down one of their starting tackles this weekend if Marcus Cannon's calf injury is enough to keep him out of action.

The team's right tackle for the first four games of the regular season was missing from the start of Thursday's workout in full pads. Cannon has been listed on the team's injury report with a calf issue since last week. He was limited for all three practices leading up to Sunday's loss with the Bills, and he was limited in Wednesday's practice of this week as well.

If Cannon does not participate on Thursday, that would could throw his availability for Sunday into doubt. Behind Cannon on the Patriots depth chart at tackle are Cameron Fleming and LaAdrian Waddle. Rookie left guard Joe Thuney played tackle as a senior at NC State, and fellow rookie guard Ted Karras saw some practice time at tackle during training camp.

Other Patriots who were not spotted at the start of Thursday's practice include linebacker Shea McClellin (concussion), defensive tackle Vincent Valentine (back) and running back Brandon Bolden (knee).