As reported by CBS Sports' Jon Heyman, the Sox "have been receiving decent trade interest in recent days" regarding their 25-year-old infielder, though they appear uninterested in dealing him just yet.
In terms of value, Middlebrooks is likely about as low as he'll get right now, with his slow start to the season (.629 OPS in 82 plate appearances), his struggles last year (.271 OBP) and his injury earlier this year, when he fractured his right index finger.
It's understandable, then, that Sox general manager Ben Cherington is ostensibly reluctant to deal Middlebrooks given the lack of return his club would receive. Also, as Heyman notes, a strong second half might allow the Sox to make a move for slugger Giancarlo Stanton, with the Marlins showing interest in Middlebrooks last winter, according to Heyman.
Some type of Middlebrooks-Stanton swap seems especially far-fetched because the Marlins have made it clear in the past that they want to build around their star outfielder, meaning it would take significantly more than just Middlebrooks to make that deal work. Even with a star-studded farm system, the Sox might have enough to match the Marlins' demands, but the latter could demand so much in return that a trade could be unrealistic.
Putting Stanton aside, Middlebrooks is certainly an attractive player for teams in need of a third baseman, especially one with demonstrated power and perhaps the ability to hit for some average. Though he hasn't quite been able to match his .288 batting average from his rookie season, Middlebrooks has shown some pop for the better part of his career, with 34 homers in just over a season of at-bats—686, to be exact.
In terms for a timeline, Middlebrooks started his rehab assignment on Tuesday and has three hits in 12 at-bats, including a homer and a triple, though he went 0-for-4 with three strikeouts on Saturday. He did play in the field on Friday for the first time during his rehab stint, but he appears to still have some time left in the minors as he continue to heal.
Once Middlebrooks makes it back to the majors and has an opportunity to prove himself again, the Sox could re-think their refusal to deal him should he heat up down the stretch.