That was originally supposed to be Lester's start, but manager John Farrell felt it was best to let Thursday's non-waiver Trade Deadline pass before having the ace pitch.
As for Doubront, his lack of consistency over the last three seasons led to his move to Chicago.
Doubront was vocal with his dissatisfaction about his move to the bullpen earlier in the season, and there were plenty of people within the organization who wondered if that impacted his focus and performance as a reliever.
Perhaps Doubront will benefit from a move to the National League.
"I don't necessarily buy into the change of scenery," Farrell said. "But as I talked with him a little bit a while ago, if this does come to fruition, the work is always going to be needed, regardless of where you pitch or the role in which you're pitching in. He has performed well for us over a period of time, and it can't be understated the importance of his relief appearances last year in the World Series. Those were two pivotal outings by him, and he did a great job."
In 17 appearances this season, 10 of which were starts, Doubront went 2-4 with a 6.07 ERA.
Signed by Boston as an amateur free agent in 2005, Doubront made it to the Majors in '10.
In 98 games over five seasons, the lefty went 26-22 with a 4.82 ERA.
He became a starter in '12 and took a regular turn in Boston's rotation for two seasons. But in both of those years, Doubront faltered badly down the stretch.
Though Doubront wasn't happy about his move to the bullpen last October, he pitched well in the postseason, going 1-0 with a 1.29 ERA in four outings.