SAN FRANCISCO -- Mario Manningham is out. Joe Staley and Brandon Jacobs are in. Those were the most meaningful developments for the San Francisco 49ers as their NFC West opener against Seattle neared Thursday night.

A shoulder injury will prevent Manningham from playing. Staley is expected to start at left tackle after suffering a concussion against the New York Giants four days ago.

Jacobs, inactive since suffering a knee injury in August, will join Frank Gore and Kendall Hunter as the halfbacks active for San Francisco. Rookie LaMichael James is again inactive.

The 49ers are keeping four wide receivers active. They have kept five active in each of their last three games as well as for the season opener. They had four active for the other two games.

Michael Crabtree will start. Randy Moss is set to start at the other spot if the 49ers. Kyle Williams is another candidate. Return specialist Ted Ginn Jr. is the fourth wide receiver active. He hasn't been a factor in the offense to this point.

The 49ers have three halfbacks and three fullbacks active for this game. I would expect them to lean heavily on personnel groupings with two backs and fewer than three wide receivers. That is their nature in general. They will want to establish their ground game even though Seattle's run defense has been strong.

Last season, the 49ers averaged 14.4 yards per pass attempt when using two backs and one tight end against the Seahawks' base defense, according to ESPN Stats & Information.

The 49ers have generally had success passing from run-oriented groupings and formations. They are averaging 6.8 yards per play overall on first down, third-best in the league. The Seahawks are allowing 4.8, sixth-fewest.