Yankees manager Aaron Boone called Judge's injury a "very mild strain of his calf." He said an MRI taken during Thursday's off day revealed the ailment.
"He wants to be out there and feels like it's a day-to-day thing, which it very well may be," Boone told reporters Friday. "It goes without saying how important a player Aaron is to us. I think it's really important that he not go out there and hurt this thing significantly trying to play through something."
Judge's trip to the injured list is retroactive to Wednesday, meaning the earliest he could return would be Aug. 21 against the New York Mets at Citi Field. Infielder Thairo Estrada was recalled from the team's alternate training site in a corresponding roster move.
The Yankees slugger was removed for a pinch-hitter in the sixth inning of Tuesday's game against the Atlanta Braves. He didn't play in the series finale Wednesday.
"When I took him out, it was basically my observation," Boone said. "I didn't consult with any trainers at that point. It was me and a couple of coaches watching him in the outfield moving around. I just felt like he wasn't moving like he normally would, so I made the decision right there.
"Later [Tuesday] night, we dove into the treatments he's getting, how he's feeling. The next day we decided, OK, we need to probably go through a battery of tests with this."
Entering play Friday, Judge led MLB in home runs (nine), RBIs (20) and slugging percentage (.758).