The San Francisco 49ers got a piece of troubling news concerning linebacker Randy Gregory on Sunday ahead of their highly anticipated Christmas Day showdown with the Baltimore Ravens.

Gregory, who had not appeared on the Niners' injury report this week, showed up on Sunday because of an illness, per The Athletic's Matt Barrows. The illness is serious enough that Gregory is questionable to play on Monday.

Losing Gregory would be a significant blow to San Francisco's depth on defense. The former Dallas Cowboys and Denver Broncos rusher has emerged as an important rotational piece for Steve Wilks's unit.

The 2015 second-round pick out of Nebraska began the 2023 season with the Broncos. But he was deemed expendable after a rocky start for Sean Payton's team led to a renewed focus on developing younger players.

Gregory has appeared in nine games for the 49ers this season. He got his most extensive amount of work in Week 15 against the Arizona Cardinals. For the first time as a member of the San Francisco 49ers, Gregory played more than 50% of the snaps on defense.

Known for his pass-rushing prowess, Gregory has added three sacks in limited snaps as a valuable role player.

49ers' defense hoping for health

Gregory isn't the only injury concern for the 49ers along the defensive line.

49ers' Kyle Shanahan and Arik Armstead

Arik Armstead (foot/knee) has already been ruled out for Monday's clash. It will be the third consecutive game that Armstead will be forced to miss.

Defensive tackle Javon Hargrave (hamstring) sat out Week 15 as well. But the star returned to practice on Friday, giving him a chance to suit up on Monday.