Arik Armstead missed all of practice the week leading up to the 49ers game against the Ravens on Christmas, which points to him not playing.
Currently, the Niners defense is vulnerable against the run, as the red birds managed to gouge coordinator Steve Wilks' side of the ball to the tune of 234 rush yards, the most San Francisco had given up on the ground since 2017.
A big reason why was the 49ers were down two of their starting defensive linemen, Arik Armstead and Javon Hargrave, who were out with foot and hamstring injuries, respectively.
Now, the Niners are poised to host the 11-3 Baltimore Ravens on Christmas for Monday Night Football, and Baltimore just so happens to lead the entire NFL in rushing.
San Francisco's ability to stop the run, or even just slow it down, will be a massive X-factor in determining the primetime game's outcome.
Unfortunately, it doesn't appear as if Armstead will be able to participate.
Javon Hargrave returns to final 49ers practice, Arik Armstead still out
Armstead has been dealing with foot and knee injuries since before the 49ers' Week 13 win over the Philadelphia Eagles, and he had to exit that particular game halfway through and did not return.
He also hasn't played in the two games since.
After missing the first two days of Niners practice ahead of Monday's contest, Armstead was noticeably absent from Saturday's practice, too, backing up head coach Kyle Shanahan's comments from earlier in the week that said the defensive tackle was "a little bit more of a longshot."
Armstead has 27 tackles and five sacks on the year but is at risk of missing his third game in a row.
Hargrave, meanwhile, did return to practice after missing Thursday's practice, and that'll be a significant boost against quarterback Lamar Jackson and a Baltimore squad that's averaging 5.0 yards per rush on the year.
Update: The Niners have ruled Armstead OUT for Monday's contest. Hargrave is questionable.
The 49ers and Ravens kick off on Monday, Dec. 25 at 8:15 p.m. ET from Levi's Stadium.