PITTSBURGH -- Red Sox utilityman Brock Holt is not expected to face the Pittsburgh Pirates -- the team that drafted him in 2009, gave him his first big-league exposure in 2012, then traded him to the Sox in December of the same year -- during this week's interleague series.

Holt missed his 10th game Tuesday night with concussive symptoms and is scheduled to undergo more tests Thursday at the University of Pittsburgh Medical Center for Sports Medicine, where Dr. Micky Collins last week first diagnosed the symptoms.

"While he's improving, he's still going through some vision exercises," Red Sox manager John Farrell said. "He has a re-examination and a battery of tests scheduled for Thursday with Dr. Collins. I think that will be a pivotal day -- a pivotal day in the sense of where he's at and the projection for him going forward.

"Until we get that information, I have no real date marked for when he can be on the field. He'll be on the field when he's ready, but Thursday is going to tell us a lot."

Holt’s condition has been traced back to a ninth-inning collision he had with second baseman Dustin Pedroia in Toronto on Aug. 25, when Holt took a shot in the head from Pedroia while both were in pursuit of a ground ball hit up the middle by Jose Reyes.

Holt said he felt discomfort, but continued to play until his condition worsened. The Sox finally shut him down after the game of Sept. 5, and last week he was sent to Pittsburgh, where Collins made his diagnosis.

Holt, who was batting .300 as late at Aug. 18, batted just .200 (9-for-45) in the 10 games after he collided with Pedroia. He still has posted an impressive slash line of .281/.331/.381/.711, with a WAR of 2.2, on the season.