Joe Staley back on practice field

SANTA CLARA, Calif. -- In a bit of surprise, San Francisco 49ers left tackle Joe Staley practiced Thursday during the media's allotted time at the beginning of practice.

It is a sign that Staley may be able to play Sunday in a crucial game against NFC West rival Seattle. Staley suffered a right knee injury Sunday against St. Louis in the first quarter and did not return. It was initially expected that he would miss a game or two. He did not practice Wednesday, when coach Jim Harbaugh said he would not rule whether Staley could play against Seattle.

With Staley on the practice field Thursday, his chances of playing Sunday increase highly. Barring a setback, there appears a solid chance he can play.

If Staley plays, right guard Alex Boone will stay put at left tackle. He replaced Staley against the Rams while the inexperienced Joe Looney played right guard.

While Staley made progress, the same can't be said for left guard Mike Iupati. He remained out of practice and has missed the past two games with a knee sprain. Adam Snyder has been playing in his place.

The 49ers will need to be as close to full strength as possible against Seattle. The 49ers have surrendered half of their 30 sacks this season in the past four games.