Hasselbeck suffered a hip injury during Seattle's next-to-last regular-season game and did not play Sunday in the victory over St. Louis that put the Seahawks in the playoffs.
Charlie Whitehurst, who started only his second game as a professional, completed 22-of-36 passes for 192 yards and the game's only touchdown in the 16-6 win over the Rams.
Seattle enters the playoffs with a losing record, having dropped seven out of nine games prior to the win against St. Louis.
Hasselbeck threw for 3,001 yards and 12 touchdowns in 14 starts this season. He was intercepted 17 times.
This is his 12th year with the Seahawks. He led them to the NFC championship in the 2005 season.