The bullpen currently includes two proven righty setup men in Brad Ziegler and Junichi Tazawa, in addition to the emerging Matt Barnes. Those three relievers are probably going to stick with the club under any circumstances.
There are also two veteran starters who were recently moved to the 'pen in Joe Kelly and Clay Buchholz. Kelly still has Minor League options, but the Red Sox might be leery of sending him back down so soon after he was called up.
Buchholz is in the final season of his contract, and could possibly be moved to a club in need of a starter.
Two lefties fill out the bullpen -- Robbie Ross Jr. and Tommy Layne.
Ross has options, while Layne does not.
Do the Red Sox need two lefties in the bullpen?
"It probably depends on the team we're going up against," said manager John Farrell. "You'd like to have it. Whether or not that becomes a little negated because of the [three] left-handers we have in the rotation now [remains to be seen].
"But Tommy has shown the ability, as he did last night, to get one lefty hitter. Robbie has even been more successful this year against lefties than in year's past, so you'd like to have two if you've got to match up in those middle innings."
Kimbrel, who underwent surgery to repair a torn meniscus in his left knee on July 11, made 17 pitches in a rehab appearance for Triple-A Pawtucket on Saturday. He will rejoin the Red Sox in Seattle on Monday.
Ian Browne has covered the Red Sox for MLB.com since 2002. Follow him on Twitter @IanMBrowne and Facebook. This story was not subject to the approval of Major League Baseball or its clubs.