The Minnesota Vikings have ruled out running back Adrian Peterson for their final game of the season.

The Vikings announced Saturday they downgraded Peterson from doubtful on the original injury report to out against Detroit today, when the Vikings and Lions will play the last game at the Metrodome.

Peterson sprained his right foot Dec. 8 at Baltimore and sat out the following week against Philadelphia. He played last Sunday at Cincinnati but was mostly ineffective. Peterson acknowledged afterward the injury affected his performance. He has also been bothered this year by a sore groin.

Peterson finished the season with 1,266 yards rushing, the second-lowest total of his seven years in the NFL.

BEARS KEEP FULLBACK — The Chicago Bears signed fullback Tony Fiammetta to a two-year extension that will keep him with the team through the 2015 season.

Fiammetta has appeared in each of the Bears’ first 15 games in his first season in Chicago, helping running back Matt Forte total 1,229 yards rushing — nine short of Forte’s career high set in 2008. The Bears close the regular season Sunday against Green Bay.

The fifth-year fullback has totaled 26 yards rushing and 12 receptions for 130 yards over his career with Carolina, Dallas, New England and Chicago.

AROUND THE LEAGUE — The New England Patriots signed safety Kanorris Davis and defensive back Justin Green from the practice squad to the 53-man roster Saturday. Davis, a linebacker in college at Troy, has played two games on special teams this season. Green, from Illinois, played in New England’s victory over Denver on Nov. 24. … Seattle Seahawks cornerback Walter Thurmond insists he’s ready to play and that he hasn’t lost a step. Thurmond is returning from a four-game suspension for violating the league’s substance-abuse policy, reportedly for marijuana. Thurmond had a breakout year before his suspension, but he watched Byron Maxwell hold his own in Thurmond’s place. Coach Pete Carroll said Maxwell would start Sunday against St. Louis. To make room for Thurmond, the Seahawks waived cornerback Perrish Cox. For now, at least, the Seahawks have decided to keep injured wide receiver Percy Harvin (hip) on the 53-man roster. … Green Bay Packers receiver Randall Cobb was activated from injured reserve and has been listed as questionable for today’s crucial game against the Chicago Bears. Cobb was the team’s allotted player on injured reserve who was designated for return after getting hurt during a 19-17 win Oct. 13 at Baltimore. The playmaking wideout was added to the injury report Saturday with a knee injury. Cobb caught 29 passes for 378 yards and two touchdowns playing the first five games this season for Green Bay (7-7-1).