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6/22/2013 11:39 P.M. ET

Progress delayed, Buchholz won't start Tuesday

DETROIT -- Clay Buchholz has missed another target date to return. The unbeaten ace was limited to flat-ground work on Saturday instead of throwing a bullpen session, and has therefore been ruled out of a return on Tuesday night.

In fact, because Buchholz has now gone two weeks without pitching in a game, it's likely he'll have to go on a Minor League rehab assignment before returning to the Red Sox.

"Obviously, right now, he's not going to start Tuesday, so basically what we're doing is going as tolerated with throwing," said Red Sox manager John Farrell. "It's likely that at some point we're probably going to have to get him out on a rehab assignment, at least one start for now, but there's no time frame for that. We've got to get him on the mound first and build from there."

Buchholz, who is 9-0 with a 1.71 ERA in 12 starts, is frustrated by the way things are going.

The right-hander injured his right AC joint due to an awkward sleeping position after his start on May 22. Buchholz returned to face the Yankees in a rain-shortened shutout on June 2 and beat the Angels on June 9, but had to leave that start when he developed discomfort in his neck.

"I felt better [throwing on Saturday], but not quite to the point of getting off a mound right now," Buchholz said. "I'm still trying to feel it out. It's taking a lot longer than I want it to. I'm definitely making progress in the right direction. The intensity went up today without any more soreness than yesterday or the day before. Like I said, I'm moving forward -- just not on as quick a pace as I'd like."

There is improvement, but it's more gradual than Buchholz would prefer.

"It's getting better every time I go out," Buchholz said. "There's always one certain spot during the day, when I make a throw or try to put a little more effort into it, it's not a sharp pain but it's definitely something that I feel. If I was to throw 100 percent, it would be a little more intense. I want to be 100 percent off the mound before I get into a game."

Allen Webster was called up from Triple-A to fill in for Buchholz on Saturday night against the Tigers. Alfredo Aceves has been effective three times as a spot starter in recent weeks.

Morales could be headed back to DL

DETROIT -- Franklin Morales continues to have a tough time staying healthy.

The lefty reliever departed Saturday night's 10-3 loss to the Tigers with discomfort in his left shoulder, and could be headed to the disabled list.

"He'll be reexamined here when he comes in [Sunday]," said Red Sox manager John Farrell. "Potential for a DL."

Morales pitched 2 1/3 innings, giving up five hits and four runs. He came out with two outs in the seventh.

The disabled list is where Morales was when last season ended, and when this season started.

"On one pitch, I felt a little something," said Morales.

Morales didn't start his 2013 season until May 30. Saturday was his sixth appearance of the season.

"That's crazy, man. But, I stay positive," said Morales.

Iglesias' play has Middlebrooks in bench role

DETROIT -- The Red Sox are now at the point of the season where statistics are tough to ignore, and roles are starting to define themselves.

Quite simply, Jose Iglesias (.431 average in 102 at-bats) has turned into the primary option at third base while Will Middlebrooks (.192 average in 203 at-bats) has been reduced to a bench role.

It was an open competition when Middlebrooks returned from the disabled list on June 10. But since then, he has continued to struggle while Iglesias keeps hitting.

Against left-handers, there will still be times when Iglesias subs for Stephen Drew at short, giving Middlebrooks a chance to start at third.

Will there come a time when it might make more sense for Middlebrooks to be optioned to Triple-A so he can play regularly?

"We talk about a lot of different things -- [general manager] Ben [Cherington], myself, others," said Sox manager John Farrell. "We went from, 'If Iglesias stays, how many days a week can he play and still maintain his development?' And now we're flipping that with Will. If there comes a point where we feel like he's not getting enough reps, maybe that comes into the discussion a little bit more, but that's not imminent right now."

Middlebrooks is trying to do what he can to stay sharp so that he can perform well if called on. It was a year ago that Middlebrooks had played so well that veteran Kevin Youkilis was forced to a bench role, and eventually traded.

"That's just the way the game is," Middlebrooks said. "All I can do is bust my [butt] to get back to where I was."

Middlebrooks hopes he doesn't have to return to the Minors, but he's not focusing on that right now.

"I can't worry about that," Middlebrooks said. "I'm really trying not to worry about what I can't control. All I can control is how hard I work every day. That's all I'm worried about."

Carp gets start at first as Napoli gets break

DETROIT -- Mike Carp, who hadn't played in six days because of right hamstring tightness, started Saturday night's game at first base. Mike Napoli, who was sidelined last weekend by an illness, got the night off.

Red Sox manager John Farrell said this was simply a day off for Napoli.

"It is, yeah," Farrell said. "Mike Carp is ready to go, physically, after the hamstring cramping he had down in Baltimore. Matchup, [it gives us] another left-hander in there [against Max Scherzer]. We're not sure how much they'll have left-handed relief available for them."

Carp has done a fine job in a bench role this season, hitting .324 with eight homers and 25 RBIs in just 105 at-bats entering play Saturday.

Given that Daniel Nava has been slumping of late and could be in need of some rest, that could give Carp some more opportunities.

Nava entered Saturday with just one hit in his last 20 at-bats.

Anything Farrell has seen with Nava?

"A swing getting a little bit long," Farrell said. "This is probably the most consecutive games played at this level for quite a while, and we're mindful of that. We have to pick spots when needed. That's what's been the beauty of this bench. We've been able to rotate guys in and out and get some regular work in a number of different spots. That might be something that's coming as well with Daniel."

Ian Browne is a reporter for MLB.com. Read his blog, Brownie Points, and follow him on Twitter @IanMBrowne. This story was not subject to the approval of Major League Baseball or its clubs.