It's possible the Red Sox could call up a fifth starter before May 20. At this point, Farrell basically needs a temporary rotation member to bridge the gap until David Price returns, which could be by May 24 or 29.
"We'll determine when that fifth starter will be inserted," Farrell said. "There's a couple of things we may look to do. With both Chris and Rick working deep into games, one approach we could take is to insert someone in between those two guys to spread out the bullpen, or just add the fifth starter on the back end. That's all kind of in the works right now."
This weekend, Porcello will pitch Friday against the Rays, followed by Sale on Saturday. The co-aces have pitched back-to-back all season. A few times, the lack of innings from the other pitchers in the rotation has led to an overworked bullpen.
Lefty Brian Johnson and righty Hector Velazquez are the most likely options at this point to be called up from Pawtucket to fill out the rotation before Price gets back.
Once Price returns, the Red Sox will have a rotation of four lefties and one righty (Porcello).
"Yeah, there's a couple of candidates I think are probably ahead of the group," Farrell said when asked about the potential callup to the rotation. "The one thing you have to look at is, 'Do we want four straight left-handers, or do we kind of mix a right-hander in there?' These are things that are all being taken into account looking at the matchups. You've got a little bigger ballpark in Oakland to deal with. So while we'll take the best pitcher who is pitching the best, we'll also factor in the other things we mentioned."
"Some of the symptoms he had last night, the spasming, has kind of relieved itself somewhat," Farrell said before Thursday's game against the Brewers. "He's still going to need some more treatment here this morning. [It's] questionable whether he's going to be available later on to pinch-hit, so that's completely up in the air right now."
• While Carson Smith is making enough strides in his return from Tommy John surgery that he could face hitters by next week, Tyler Thornburg continues to make slow progress in his attempted return from a right shoulder impingement. Both righties could be key to Boston's bullpen this season.
"It's been a little bit of a puzzle for all involved here -- including Tyler -- because the MRI's that he's gone through, while showing a little bit of an impingement, hasn't revealed anything more structural than that," Farrell said. "So while the inflammation has been kicked out of there and been subsided, he's still not over the hump, so to speak, to the extent we would have anticipated. I can't tell you there's additional testing scheduled, but we're still working through to get the arm strength built up."
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.