Thurmond injured his hamstring during practice Wednesday and has been officially ruled out. The Seahawks will be forced to start their third cornerback in as many weeks against the Bills.
"Walter's doing it day-to-day," head coach Pete Carroll said. "On this day, he can't go."
Either Byron Maxwell or rookie Jeremy Lane will start for Seattle, with both expected to play extensively. Brandon Browner started Seattle's first 11 games before being suspended for a violation of the league's performance-enhancing drug policy. Thurmond started last week in place of Browner before tweaking his hamstring in practice.
Seattle had used only three cornerbacks through the first 11 weeks of the season: Browner, Richard Sherman and Marcus Trufant. Trufant has missed the last two games with a hamstring strain and has been ruled out as well for Sunday's game. Now Seattle is down to its fifth and sixth options at the position.
Both Maxwell and Lane played extensively in the Seahawks' 58-0 win over the Arizona Cardinals last week.
"They've been playing a lot on special teams but it's different play after play," Carroll said. "The guys did well last week and they got extensive play so it's important and we feel better about that because of it."
Wide receiver Sidney Rice returned to practice Friday after missing the first two days of practice this week with a bruised foot. Rice was in a walking boot Wednesday but was able to get work in during Friday's practice and is expected to play. Receiver Charly Martin suffered a serious injury to his calf in practice on Thursday and is expected to be placed on injured reserve. The team has yet to make a move to fill Martin's place on the active roster.
Safety Kam Chancellor and defensive end Red Bryant were full participants in practice and are listed as probable. Running back Marshawn Lynch was limited with back and foot injuries but is also expected to play against the Bills.