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Broncos starting center Dan Koppen was “carted off with [a] leg injury” on Sunday, Mike Klis of the Denver Post reported.

The nature and seriousness of the injury is not known.

Koppen, 33, started 12 games for the Broncos in 2012 in place of J.D. Walton, who suffered a broken ankle vs. Oakland on Sept. 30. Walton had offseason surgery on the injured ankle and is on the active / physically unable to perform list.

UPDATE 2:51 p.m. ET: Guard Manny Ramirez is the Broncos’ center for the time being, according to Klis. Per the Post, reserve center C.J. Davis suffered a leg injury Saturday, further stressing the depth at center at least in the short term.