The San Francisco 49ers' defensive line is on a hot streak entering their massive Week 13 game with the Philadelphia Eagles, but it could be without a key piece for a contest that could go a long way to deciding the final seeding for the NFC playoffs.

After a day off on Tuesday, the 49ers returned to the facility for practice on Wednesday as they prepare to face the 10-1 Eagles in a rematch of the NFC Championship Game from last season.

But one player whom head coach Kyle Shanahan confirmed would not practice is defensive tackle Arik Armstead.

The 2015 first-round pick was not seen during Monday's bonus practice and Shanahan revealed he is dealing with a foot injury.

There was positive news on the opposite side of the trenches, with Spencer Burford set to practice in a limited capacity after missing the win over the Seattle Seahawks on Thanksgiving with a knee injury.

A potentially huge setback

It is not clear at this point whether Armstead will be available to face the Eagles, but a potential absence would be a massive blow to the 49ers.

Armstead is enjoying one of his finest seasons since 2019, when he recorded a career-high 10 sacks.

Through 11 games, Armstead has five sacks and 13 quarterback hits. His 36 pressures are 13th among interior defensive linemen, according to Pro Football Focus. Twenty eight of those pressures have come on true pass sets, putting him tied ninth alongside defensive tackle running mate Javon Hargrave, former teammate DeForest Buckner and Zach Sieler of the Miami Dolphins.

Armstead is seventh in PFF pass rush grade, four spots behind Hargrave, with their partnership reviving an interior pass rush that was too often dormant last season, including in a title game in which the 49er defense was left fighting an uphill battle because of a lack of offensive support. An elbow injury to Brock Purdy on San Francisco's first offensive series, followed by Josh Johnson's concussion, left the Niners without a healthy quarterback and any credible offensive threat.

Hargrave was on the opposing sideline on that occasion. If Armstead cannot go, the former Eagle will likely partner Javon Kinlaw on the starting defensive line.

Kinlaw does not have any sacks this season but the 2020 first-round pick has enjoyed a more encouraging year after several injury-hindered campaigns and is 14th in pass rush grade.

With Nick Bosa and Chase Young quickly forming a devastating edge rush partnership following the latter's arrival at the trade deadline, San Francisco will be hopeful of its pass rush continuing to excel even against Philadelphia's strong offensive line, but the prospect of them doing so will be much more likely with Armstead on the field.

Will you be able to watch 49ers-Eagles on TV?

It’s essentially a national game.