Flacco's hip injury has put his status in question for the Ravens' pressure-filled game against the Cincinnati Bengals on Nov. 18, a source confirmed to ESPN.
If Flacco is sidelined, the Ravens could start Jackson, their rookie first-round pick. Flacco is undergoing tests to determine the severity of the injury, according to multiple reports.
If the Ravens don't believe Jackson is ready to start, another option is Robert Griffin III. Baltimore has carried Griffin on its 53-man roster because of his starting experience.
Flacco injured his hip in the opening series of Sunday's 23-16 loss to the Pittsburgh Steelers. He didn't miss any plays and said after the game that the injury didn't affect him.
It's become a tumultuous bye week in Baltimore, where the Ravens (4-5) have lost three straight and questions are swirling about coach John Harbaugh's job security. A loss to the Bengals would significantly diminish Baltimore's playoff chances.
Flacco's injury adds to the Ravens' increasing drama at quarterback. Harbaugh said this week that he wanted to see more of Jackson on the field, though he indicated he would stick with Flacco as the starter for "right now."
Jackson, who has been used in specialty packages, is the only one of the five quarterbacks selected in this year's first round yet to make a start.
Flacco, 33, is in the midst of another underwhelming season since winning the Super Bowl six years ago. He has thrown 12 touchdown passes and six interceptions for a 84.2 passer rating, which ranks No. 26 in the NFL.
Durability has been one of Flacco's strengths. He has missed six games in his 11-year career, starting the past 41 games. But Flacco repeatedly has been banged up in recent years, from tearing knee ligaments to herniating a disc to injuring his hip.
The Ravens essentially put Flacco's starting role on notice when they traded up in this year's first round to select Jackson with the No. 32 overall pick. Jackson, the 2016 Heisman Trophy winner, became the only player in FBS history to rush for at least 1,500 yards and pass for at least 3,500 yards in a season.
In the preseason, Jackson looked raw in throwing the ball, completing 50 percent of his passes. In nine games this season, Jackson has primarily run a Wildcat-style offense, throwing 7 of 12 passes for 87 yards and a touchdown while ranking second on the team with 139 yards rushing. His biggest challenges have been improving his accuracy and throwing from the pocket.
The Ravens would be turning to Jackson in the midst of Harbaugh's most pivotal season. Harbaugh's 11-year run could end if Baltimore fails to make the playoffs for a fourth straight season.
This also could be Flacco's final season in Baltimore. The Ravens can create $10.5 million in cap space by cutting him after the season or free up $18.5 million in space by designating him as a post-June 1 cut.
The Athletic was the first to report news of Flacco's uncertain status.
ESPN's Adam Schefter contributed to this report.