Manager Aaron Boone said Saturday that Stanton strained his left calf while running the bases, Jorge Castillo of ESPN.com reports.
Stanton has been on the injured list since late April due to a strained right calf, and he is now dealing with a left calf strain as well after 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 year.