Earlier in the day, Red Sox manager John Farrell mentioned that the third baseman's rehab assignment could be longer than just four games.
The Red Sox want to make sure his swing is right before he returns to action.
In a meeting with Middlebrooks, Farrell emphasized some things beyond just proving he's healthy.
"[A chance] to get his timing back," Farrell said. "But then also let's use this as an opportunity to get a little momentum going before he comes back. We're hopeful that that is sooner rather than later. Saturday is still the day in which he's first eligible to be activated. It could very well be Saturday. It could be shortly thereafter."
The Red Sox have also been challenged against left-handed pitching this season. Entering Wednesday, they were tied for 20th in the Majors with a .241 average against lefties, while ranking first with a .288 average against righties. A healthy, productive Middlebrooks could add a dangerous threat against southpaws.
"I think the most important thing is our need for right-handed bats in this lineup to balance out our left side of the plate," Farrell said. "He's a vital part of that. We want to make sure he's got some momentum coming back to us with."
This sophomore season has been an inconsistent one for Middlebrooks. He is hitting .201 with eight homers and 21 RBIs.
"This isn't going to be based on batting average [at Triple-A]," said Farrell. "I think it's more important that as he was showing more consistently before the injury, the ability to drive the ball into right-center field. As we've talked many times over, that's when he's at his best. [He just needs] to take his normal, natural approach and repeat it. That's what we're looking for."
Meanwhile, Jose Iglesias has been holding down the fort at third base both offensively and defensively during the absence of Middlebrooks.
"I wouldn't say this is predicated just on what Jose is doing," said Farrell. "Bottom line is, I mentioned to Will, what's best for Will is best for us. And that's to get him in a position where he's swinging the bat good and he's feeling confident about himself. He's our third baseman. He will come back to us in that frame of mind and with that ability to swing the bat. We're going to be a better team because of that."
Ian Browne is a reporter for MLB.com. Read his blog, Brownie Points, and follow him on Twitter @IanMBrowne. Jason Mastrodonato is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.