Just one day after returning to the field, Pittsburgh Steelers' strong safety Troy Polamalu missed the Thursday afternoon practice, and there is now some uncertainty about his status for the Sunday night matchup at New England.
"We'll see how he is [on Friday]," coach Mike Tomlin said.
Pittsburgh does not have to officially list Polamalu's status until issuing the mandatory Friday injury report.
The three-time Pro Bowl performer missed the past two games with a sprained knee, but participated in practice on Wednesday, and Steelers officials seemed optimistic that the five-year veteran would return to the lineup. Tomlin did not provide a reason why Polamalu did not practice and declined to say of his absence represented a setback in his recovery.
Polamalu, 26, injured his knee in the Nov. 18 overtime loss to the New York Jets.
If he is unable to play at New England, eight-year veteran Tyrone Carter, who has started the last two games, would replace Polamalu again. The Steelers are already playing without Ryan Clark, their starting free safety, who was placed on injured reserve last month after having his spleen removed.
Carter has performed well in Polamalu's absence, but does not have the versatility of the Steelers' most flexible defender.
Unlike most teams, the Steelers do not play a nickel alignment on third down, relying instead on a dime scheme, and Polamalu is critical to that coverage package. The five-year veteran functions as a hybrid linebacker-safety in the third-down package and often blitzes from the dime look.
Pittsburgh defensive coordinator Dick LeBeau has been using rookie linebacker Lawrence Timmons, the team's first-round choice, to replace Polamalu in the third-down package.
In nine games this season, Polamalu has 42 tackles, seven passes defended, two forced fumbles and a fumble recovery.
Senior writer Len Pasquarelli covers the NFL for ESPN.com.