"Improved," said manager John Farrell. "Yet not ready to go today. We're shooting for Tuesday."
Farrell said the Red Sox were not trying to hold Ellsbury back.
"No, it's the assessment of the medical staff, how he's responded to treatment," said Farrell. "It's improving, but he's not ready to get on the field."
Ellsbury suffered the injury on Thursday night in Philadelphia, where he stole a career-high of five bases.
Ian Browne is a reporter for MLB.com. Read his blog, Brownie Points, and follow him on Twitter @IanMBrowne. This story was not subject to the approval of Major League Baseball or its clubs.