The former pitcher for the Red Sox told ESPN that “his body just isn’t up for the rigors of a major league season anymore.”
Lester, 38, won World Series titles with the Red Sox in 2007 and 2013 and a third ring with the Cubs in 2016.
He split his final season with the Washington Nationals and the St. Louis Cardinals.
The Red Sox drafted Lester in the second round of the 2002 MLB draft.
He made his debut in 2006, but his rookie season was cut short when he was diagnosed with anaplastic large T-cell lymphoma. He underwent chemotherapy but was able to return to the team midway through 2007.
Lester told EPSN that his time in Boston left an impression on him.
“It makes you grow up really fast, and it’s an awesome, awesome place to me,” Lester said. “It made me more accountable than if I was somewhere else.”
The five-time All-Star finished with 200 wins and a 2.51 postseason ERA.