Casey walked and scored in the top of the second inning but did not return to the field. Boston shifted third baseman Kevin Youkilis to first base and inserted Jed Lowrie to replace Youkilis at the hot corner.
Manager Terry Francona said that he knew something was wrong when he saw Casey on third base, and after Casey scored, he told the team that he felt something in his right quadriceps.
"It wasn't horrible, but I'm sure we are going to lose him for some time," Francona said, adding that Casey would be checked out more thoroughly following the game.
Even though his bench is already thin, Francona dismissed the idea of bringing up veteran Mike Lowell. The infielder, who made a rehab start for Triple-A Pawtucket on Friday night, was placed on the disabled list on April 10 with a sprained left thumb. He was hitting .200 (6-for-30) in nine games prior to his injury.
"Out of the question," Francona said of recalling Lowell.
The skipper added that the Sox don't want to make a big mistake and further Lowell's injury, which would only compound their current infield shortage.
With Lowell and Casey unavailable for Saturday's game, the Sox will have to do some shuffling to fill the infield holes, with Lowrie and Youkilis likely starting again.
The 33-year-old Casey entered Friday's game batting .346 and had multiple hits in five of his last 10 games. His career .302 average is 16th among active players with at least 3,000 plate appearances.
Brittany Ghiroli is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.