Stanton tweaked his injured right calf while running the bases this week, and he may need to undergo more medical imaging, Bryan Hoch of MLB.com reports.
Stanton had been ramping up toward a return to action, and manager Aaron Boone suggested Saturday that the slugger had been expected to be activated during the early portion of the Yankees' upcoming homestand, which begins Tuesday. That plan is now in peril, though it's unclear at this point how much Stanton's setback will push back his timeline.