Smith, who will be listed as questionable officially, has started 185 consecutive regular-season games, the longest current streak for defensive linemen. He has appeared on injury reports in recent seasons. In each case, Smith participated fully in practice two days before the game.
The fact that Smith isn't practicing Friday breaks the pattern. He is one of a league-high 10 defensive starters for the 49ers to play at least 90 percent of the defensive snaps this season. His expected absence from the lineup Sunday would weaken the 49ers' defense and test the team's depth along the line.
Ricky Jean Francois would start at right defensive end. Jean Francois has been a valuable backup for his ability to play all three positions on the line.
Smith and fellow defensive end Ray McDonald (92.7 percent snaps) are mainstays on the line. Nose tackle Isaac Sopoaga (29.4 percent) has played relatively little, in part because the 49ers have spent long stretches in their nickel defense while facing a string of pass-oriented offenses. Jean Francois (16.3) is the only other defensive lineman to get meaningful snaps for the 49ers this season.
Smith (93 percent), McDonald (94.7 percent) and Sopoaga (42.1 percent) were the only defensive linemen to play for the 49ers against Seattle in Week 7.