Lester was scratched from Wednesday's scheduled start because of what manager John Farrell called "all the uncertainty surrounding" him.
Lester and Lackey have each made 21 starts this season. Lester's ERA is 2.52 and Lackey's is 3.60.
Lester has said that he would be open to re-signing with Boston this winter even if the team trades him away at the deadline.
- Dan Gartland