The Denver Broncos had already ruled injured quarterback Peyton Manning out of Sunday's game against Pittsburgh, but the news that he could not practise on Friday cast further doubt on when he might return to NFL action.
The 10-3 Broncos are still on track for a playoff berth, two games clear of the surging Kansas City Chiefs in the AFC West, but can ill afford another loss as they vie for a first-round bye with New England (11-2) and Cincinnati (10-3).
Back-up quarterback Brock Osweiler has so far proved an adequate replacement for Manning, going 3-1 in four starts, but the Broncos have not exactly been sizzling in attack, scoring an average of 19 and coming off a 15-12 loss to Oakland (6-7).
They are understandably keen to get all-time NFL touchdown leader Manning back before the playoffs, provided he is fit.
Head coach Gary Kubiak indicated 39-year-old Manning, with a torn plantar fascia in his left foot, had been pulled from practice more as a precaution, after working out with the team the previous two days.
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"He came in this morning and was a little sore, so we just said, 'OK, we'll stop for the weekend and we'll go from there', so we'll pick back up on Monday," Kubiak said.
Manning has played through injury for much of the season, exhibiting a loss of arm strength that has had some observers wondering how much the five-time league MVP has left to give.
Only the top two teams in each conference earn a bye, and the Broncos enter the critical stretch facing the Steelers (8-5) and then the Bengals, before wrapping up the regular season against the struggling San Diego Padres (3-10).
