Victorino has experienced ongoing issues with his back. Middlebrooks has continued swelling in his fractured right index finger, which has impacted his throwing.
Red Sox manager John Farrell said neither player will participate in baseball activities for the foreseeable future.
Victorino, who was examined in Boston on Thursday, is receiving treatment for discomfort in his lower back, Farrell said. In a related move, according to Farrell, hot prospect Mookie Betts made his first start in right field for Triple-A Pawtucket on Thursday night, going 0 for 2 with two walks. He is scheduled to play there again Friday night.
Betts has reached base in all 22 games since being promoted to Pawtucket from Double-A Portland. His nine-game hitting streak ended Thursday, one in which he batted .415 (17 for 41) with six multihit games and nine RBIs.
Betts' move to right field also coincided with the promotion of veteran center fielder Andres Torres to Pawtucket after he played five games with Class A Lowell, going 4 for 19 with two doubles. Torres, who was not re-signed by the San Francisco Giants after undergoing surgery to remove bone spurs in his left heel last year, underwent a six-month rehab before signing a minor-league deal with the Red Sox earlier this month.
With Victorino out indefinitely, the team's decision to promote another outfielder probably looks to be a choice between Torres and Betts, who had not played outfield professionally until this season.
"We're just trying to get him exposure to both center and right field in the event there is some further discussion and the ultimate decision is made to bring him here," Farrell said. "That has not happened yet.''
Another possibility for a right-handed bat, suggested Alex Speier of WEEI.com, is Ryan Roberts, who is currently on a seven-game hitting streak (12-for-30, .400, including back-to-back three-hit games). But Roberts has played almost exclusively at second base for the PawSox, making just two starts in the outfield, in left field both times.
The Red Sox are currently playing with just 12 position players, one short of their stated desire of 13. Farrell hinted a roster move could come as soon as Saturday.
"The goal is to get back to 13 position players,'' Farrell said. "Whether that happens by tomorrow remains to be seen, but that's the overall goal.''