Walton out for second half with ankle injury
Walton injured his left ankle late in the second quarter against the Oakland Raiders and was helped off the field. The Broncos said he would not return.
Koppen is a free agent from New England, who joined the Broncos earlier this month after getting cut by the Patriots.
Walton had played almost every snap since his rookie year in 2010.
Copyright 2012 by The Associated Press
This story is from ESPN.com's automated news wire. Wire index
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