The Ravens announced that Lewis, who started eight games as a rookie, aggravated a shoulder injury, and it has not responded to treatment. Backup quarterback Ryan Mallett has struggled in training camp and the preseason at a time when the Ravens have expressed interest in controversial quarterback Colin Kaepernick. He completed nine of his 18 pass attempts for 58 yards and was sacked once. Dustin Vaughan and Josh Woodrum are the other quarterbacks on the roster.
Flacco signed a three-year, $66.4 million extension in March 2015.
The 32-year-old has been durable over his career, which has been spent exclusively with the Ravens.More news: Trump Doubling Down on Rhetoric Rattles South Korean Markets
In his nine National Football League seasons, Flacco has only missed six games, which all came after his ACL tear toward the end of 2015.
He threw for 4,317 yards last season - which ranked No. 7 in the National Football League - alongside 20 touchdowns and 15 interceptions.
The quarterback will practice in the preseason, but is not expected to play in the remaining preseason games.