"He had to be [taken] out of yesterday's game just because of the recurring symptoms. I know it's frustrating for Brock," Red Sox manager John Farrell said before Tuesday's game against the Cardinals. "It looked like the days leading up to yesterday he was starting to turn the corner with the way he felt, the way he swung the bat. But the onset of the symptoms caused us to remove him from the game, and Brock is a frustrated guy right now."
The Red Sox will continue to monitor Holt with the hope he can get in a steady flow of rehab games without having any symptoms.
"As the symptoms subside, yeah, that's been the path and the repetition we've gone through with Brock. So I'd like to give you a date in which he'd be back in, but it's dependent upon how he feels," Farrell said.
Starting third baseman Pablo Sandoval, out since April 24 with a right knee sprain, had another productive day on Tuesday and could start a rehab assignment with Pawtucket by this weekend.
"Now that he's back to baseball activity, we've got to get him back into game shape," Farrell said. "We're hopeful [a rehab assignment] will begin when we leave here and go to the West Coast, he'd join Pawtucket and start getting some games under his belt."
Deven Marrero started his third straight game at third for Boston on Tuesday, as he at least provides defensive stability.
Ian Browne has covered the Red Sox for MLB.com since 2002. Follow him on Twitter @IanMBrowne and Facebook. This story was not subject to the approval of Major League Baseball or its clubs.