Lamar Jackson sat out Thursday's practice because of an illness, according to the team's injury report.
Jackson could still return practice Friday and finish the week's preparation before heading to play in Cincinnati.
Missing practice is a rarity for Jackson. According to ESPN's Jamison Hensley, it's just the second practice Jackson has missed in his young career.
It seems a bit of a bug is going around, as guard Marshal Yanda missed Wednesday's practice because of an illness as well. It's that time of year in Baltimore.
"He has something he caught from his kids the last couple days," Harbaugh said of Yanda.
The last time Jackson was sick before a Bengals game, he ended up in the hospital. Jackson missed a Thursday practice last year because of bad stomach pains, returned to practice Friday and ran 26 times for 119 yards in his debut on Sunday.
Defensive tackle Brandon Williams also did not practice, though for non-injury reasons. Left tackle Ronnie Stanley (knee) was limited after sitting out Wednesday.