Flacco, 34, lost his starting job to rookie Lamar Jackson in 2018. The 11-year veteran completed 61.2 percent of his passes for 2,465 yards, 12 scores and six interceptions in nine starts last season, posting a 4-5 record as the Ravens' starting quarterback.
Reed -- who spent five seasons as Flacco's teammate -- told TMZ Sports that "it's definitely Lamar's team."
"Flacco might be in Jacksonville, man, if he want to win another Super Bowl," Reed said.
Reed added that he had doubts about Flacco being a backup.
"He's a starting quarterback in this league," Reed added. "I don't know if that's what he wants. I don't know if that's what the team wants."
Flacco owns a 96-67 record as a starting quarterback. He is the Ravens' all-time leading passer with the most passing yards, touchdowns, interceptions, wins and losses in franchise history.
Reed, 40, played 11 seasons for the Ravens before finishing out his decorated tenure with the Houston Texans and New York Jets in 2013. He was named as part of the class of 2019 Pro Football Hall of Fame inductees Feb. 2.