Michael Bowden got the turn in place of Beckett, making his second career start. Bowden pitched 2 1/3 innings out of the bullpen on Friday night, so the Red Sox won't ask him to pitch extended innings. Left-hander Dustin Richardson, who went 2-2 with a 2.55 ERA at Double-A Portland and Triple-A Pawtucket this season, was selected from Pawtucket and activated for Monday's opener. To make room on the club's 40-man roster, outfielder Chris Carter was designated for assignment.
As for Beckett, there's a strong chance the Red Sox will just skip his turn in the rotation entirely, and let him make his last scheduled start of the regular season on Saturday against the Indians.
"First of all, it's upper left, which is good," said Red Sox manager Terry Francona. "He's been feeling it. And again, this time of year, guys feel a lot. But on the plane last night, I think he tried to get comfortable and didn't. I think he thought he'd wake up and take a hot shower and go about his business. When that didn't happen, he called me, and me and [pitching coach] John Farrell were actually in there at the time.
"So it wasn't a real difficult decision to say this doesn't make sense to [pitch Beckett]. And I think he kind of agreed. So we'll try to use good judgment and let him get worked on and let that thing relax as opposed to letting him pitch through it, which he could have. It just didn't seem like today was the day to do that."
The Red Sox didn't seem to have any deep concern about the injury.
"It's just his upper back," said Francona. "It's been there for a while. We've seen it, he's pitched pretty well. We've all had it. When it happens, you want it to go away. The harder you try, the more it [lingers]. You know, we just need to try to use good judgment."
In 31 starts this season, Beckett is 16-6 with a 3.78 ERA. After a slump in late August, Beckett has rebounded in his past four starts, giving up three earned runs or fewer in each outing.
Because of injuries and ineffectiveness in other areas of the rotation in the midsummer months, the Red Sox weren't able to get Beckett much of a break. He has 207 1/3 innings on the season, already a career high.
So perhaps the one silver lining about the back problems is that it allows Beckett to rest his arm a little before the pressure of postseason sets in.
"Any time something happens, we try to make it be beneficial," said Francona. "Rather than whine about something, we'll just try to make something that was maybe a negative today and turn it into a positive. OK, how do we do that? Well, do you pitch him? We'll sit with him and the medical staff and figure out the best course of action for him, and we'll adjust to it and try not to let it affect us."
Ian Browne is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.