The most likely scenario seems to be that the team would activate right-hander Clay Buchholz from the disabled list to face the Mariners. Buchholz was with the Red Sox in Oakland and made his final rehab start Thursday after recovering from a hyperextended left knee.
"Clay is certainly a candidate, but we recognize fully that we've got to make a roster move to get him back active to us," Farrell said. "We know that when Clay comes to us, it's going to be in exchange for another pitcher.
"We get another day further, our pitching plans will start to become a little bit more clear."
If Buchholz does get the nod, Rubby De La Rosa could be the odd man out, although he made a strong case to stick around with seven innings of one-run ball on Saturday.
De La Rosa has options remaining, as does Brandon Workman, who is eligible to return from a six-game suspension on Tuesday. But Farrell has expressed his desire to keep Workman in the rotation.
With Jon Lester, John Lackey and Jake Peavy occupying three rotation spots, just two remain for Buchholz, Workman, De La Rosa and Felix Doubront. Doubront returned from the DL on Friday and is out of options.
For the moment, the Sox are content to stand pat until Wednesday, despite currently having only three available bench players.
"[On Wednesday] we would get back to ideally our normal allotment of pitchers and position players," Farrell said.
Aaron Leibowitz is an associate reporter for MLB.com.