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."
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.