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Still clinging to faint playoff aspirations, the Pittsburgh Steelers will be forced to play a third straight game without their top defender, strong safety Troy Polamalu, when they visit the Carolina Panthers on Sunday.

Troy Polamalu

Safety Pittsburgh Steelers Profile

2006 SEASON STATISTICS Tot Ast Solo FF Sack Int 67 50 17 1 1 3

A two-time Pro Bowl performer, and the centerpiece of the ever-changing 3-4 defensive fronts conjured up by coordinator Dick LeBeau, the versatile Polamalu is officially listed as "doubtful" on the league injury report. But the sprained medial collateral ligament that Polamalu sustained in a Nov. 26 loss at Baltimore precluded him from practicing at all this week and the four-year veteran conceded he will not play against the Panthers.

Pittsburgh will also be without starting free safety Ryan Clark for a second consecutive week.

Polamalu, who had never missed a game before this season, hopes to return for the final two contests of the season, but the Steelers may err on the side of caution if eliminated from the AFC wild card chase. The ligament will not require surgery.

In 11 games this season, Polamalu has 66 tackles, one sack, three interceptions, seven passes defensed and one forced fumble.

The team's first-round choice in the 2003 draft, Polamalu is one of the NFL's premier safeties and his rare versatility is his calling card. The former Southern California star is a hybrid-type defender who combines the hitting ability of a linebacker and the range and closing speed of a safety. He frequently plays close to the line of scrimmage and is often used to blitz from the inside.

"Let's be honest, he's the key to everything we do on defense," said inside linebacker James Farrior. "You just can't find anybody else like him in the league. He's kind of our heart and soul."

Seven-year veteran Tyrone Carter will start in Polamalu's spot. Rookie Anthony Smith, a third-round pick with excellent range and "ball" skills, will make his second straight start at free safety.

Thanks to a modest, two-game winning streak the Steelers are now 6-7, but probably have to win their three remaining games to have even a remote chance of securing a wild card berth.

Len Pasquarelli is a senior NFL writer for ESPN.com. To check out Len's chat archive, click here .