Irving was having the best season of his four-year career when he tore his right MCL at New England on Nov. 2. His timeline for returning to the field was four to six weeks.
With fellow linebacker Danny Trevathan (leg) already designated to return next month, the Broncos had to put Irving on season-ending IR on Thursday.
Irving finished the season with 44 tackles, including six for a loss, and a sack. He was replaced by Steven Johnson in the starting lineup.
Davis, from Sacramento State, was a special teams player for the Saints.
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