Yankees manager Aaron Boone said Saturday that Stanton sustained a moderate left calf while running the bases Thursday, Jorge Castillo of ESPN.com reports.
Stanton has been on the injured list since April 28 due to a strained right calf, but his other calf is now the bigger concern after he strained it while falling down during his most recent baserunning session. The Yankees haven't yet ruled out a return for Stanton later this season, but Boone admitted that it will be difficult for the veteran slugger to return before the end of the campaign as a result of his latest setback.