According to Pro Football Weekly, RT James Carpenter tore his ACL in practice yesterday and has been placed on injured reserve. Add to that the loss of RG John Moffitt, who suffered a season-ending knee injury in last Sunday's game against the Ravens, and the entire starting right side of the offensive line has been lost in less than a week.
Both players will require knee surgery to repair the damage, which puts their availability for next season into question. Recovering from knee surgery can take as little as six months, but nine to twelve months is a more realistic timeline. Since both players suffered their injuries in early November, I wouldn't expect to see them back until somewhere between August and November of next year.
OT Breno Giacomini is the favorite to replace Carpenter in the starting lineup. From what I've seen of him, Giacomini does not appear to be as physicaly able as Carpenter, but what he lacks in that regard he more than makes up for in attitude and tenacity. For an NFL o-lineman, playing with a chip on your shoulder is as good an equalizer as any.
For now it looks like Paul McQuistan will be Moffitt's likely replacement, given his greater experience with Tom Cable's blocking system, but I wouldn't rule out Lemuel Jeanpierre taking over the job at some point. Both were suited up and active last Sunday, but it was Jeanpierre who was asked to take over for Moffitt for the remainder of the game, not McQuistan.