Sandoval went on the disabled list with a left shoulder strain on April 13, and the Red Sox gave him an MRI exam the next day.
The Red Sox haven't disclosed what their MRI showed, other than president of baseball operations Dave Dombrowski saying that there's "a lot going on" in Sandoval's shoulder.
The veteran Sandoval lost his starting job late in Spring Training to Travis Shaw, who has backed the club's decision by playing well on both sides of the ball.
Ian Browne has covered the Red Sox for MLB.com since 2002. 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.