Falcons' Foster suffers season-ending knee injury

ATLANTA -- For the second time in three weeks, the
Atlanta Falcons have lost their starting left offensive tackle, as rookie Renardo Foster suffered a season-ending left knee injury in Sunday's loss to the New Orleans Saints and has been placed on injured reserve.

The injury to Foster left the Falcons' already shaky offensive line perilously thin, and the team on Tuesday signed free agent Terrance Pennington to bolster the position. The Falcons have a bye this week before resuming play against San Francisco on Nov. 4.

Pennington, 24, was a seventh-round pick of the Buffalo Bills in 2006. The former New Mexico standout started nine games as a rookie but was released this summer.

When the Falcons host the 49ers, they will be forced to start their third different left tackle of the season.

Starter Wayne Gandy sustained a torn left anterior cruciate ligament in an Oct. defeat at Tennessee, and that elevated Foster into the lineup. An undrafted college free agent from the University of Louisville, where he played under Falcons' first-year coach Bobby Petrino, Foster played relatively well in two starts before his knee bucked in Sunday's game.

It is not yet known when Foster will undergo surgery.

The new starter could be second-year veteran Quinn Ojinnaka, who has played sparingly, but the Falcons might also consider other options. There is a chance starting right tackle Todd Weiner could return from a knee injury after the bye, and that might allow Tyson Clabo, who has started the last two games on the right side, to move to left tackle. Or Weiner, who has played some at left tackle, might be asked to switch sides.

No matter who plays left tackle when the Falcons get back on the field on Nov. 4, he likely will be blocking for quarterback Joey Harrington, who almost certainly will return to the starting lineup after the ankle injury suffered by Byron Leftwich last week.

In his first start of the season, Leftwich was playing well and appeared to be in a good rhythm when he was sacked by New Orleans defensive end Charles Grant and sustained a sprained right ankle. While the Falcons have not addressed the precise nature of the injury, Petrino did term it "serious" and the suspicion is that it is a "high" sprain.

If that is the case, Leftwich could be sidelined for several weeks.

Len Pasquarelli covers the NFL for ESPN.com.