Harbaugh didn't give specifics on Jackson's injury, but league sources told ESPN's Adam Schefter on Tuesday that Jackson has a sprained PCL, an injury that often sidelines players for one to three weeks.
"As the week goes on, we'll see for this week," Harbaugh said Monday. "It's probably less likely for this week, but it's not impossible. Then, after that, it'll become more and more likely."
If Jackson is sidelined this week, backup Tyler Huntley would start for the Ravens (8-4), who play at the Pittsburgh Steelers (5-7) on Sunday. Huntley is 1-3 as a starter, throwing two touchdowns and four interceptions.
In Sunday's 10-9 victory over the Denver Broncos, Jackson was hurt on the last play of the first quarter when he was sacked from behind by linebacker Jonathon Cooper. It looked like Jackson's left knee was driven into the ground when Cooper landed on top of his back.
Jackson walked without a limp to the locker room and didn't play the final three quarters. Harbaugh said after the game that he didn't believe Jackson's injury was season-ending.
This would mark the second straight season that Jackson has missed a game due to injury. Last season, the Ravens lost all four games in which Jackson was sidelined with an ankle injury.
Jackson had been extremely durable in his first 3½ seasons, missing only three of his first 51 starts and none because of injury. In 2019, Jackson was held out of the finale because Baltimore had already clinched the top seed in the AFC. He didn't play one game in 2020 because of COVID-19 and he was inactive for one game in 2021 because of illness.
This season, Jackson had shown signs of some wear and tear. He missed one practice two weeks ago because of a hip injury, and he didn't finish a practice last week due to a quadriceps injury.
Since entering the NFL in 2018, Jackson has taken a league-leading 877 hits, which amounts to an average of 12.5 hits per game.
The Ravens have expressed plenty of confidence in Huntley, who led a game-winning, 91-yard drive on Sunday. Huntley's last start came in a 16-13 loss to the Steelers last season, when he was 16-of-31 for 141 yards and two interceptions. Huntley also ran for 72 yards.
Huntley is expected to take most of the reps in practice this week, according to Harbaugh.
"We run the same basic offense with both players [Jackson and Huntley], so it's not really going to change anything in terms of preparation," Harbaugh said. "[Huntley is] a player that's got a lot of dynamics to his game. He operates really well. So, if that's the way he goes [and Huntley starts for Jackson], that's the way it goes. We'll be excited to play, and our guys will be fired up."
Also on Monday, the Ravens signed quarterback Brett Hundley to the practice squad. He was with Baltimore during training camp. With Jackson injured, the only healthy quarterbacks for Baltimore were Huntley and Anthony Brown (practice squad).
In other news, the Ravens signed 36-year-old wide receiver DeSean Jackson to the active roster. Baltimore had run out of its practice squad elevations on Jackson, who has five catches for 100 yards in three games with the Ravens.