The switch-hitting Alcantara was hitting .377 in 13 games with Nashville after being sent down June 29.
"He has been swinging the bat well," A's manager Bob Melvin said. "As we've said before, if the guy is playing well, we want to get him here and get him in the lineup right away."
Alcantara, 24, went 2-for-8 (.250) in three games with the A's in June. He can play both the infield and outfield and is speedy, as he currently leads the Pacific Coast League with 28 stolen bases.
It's unclear how long Alcantara will remain in Oakland. The A's don't have a starter scheduled for Sunday and will likely need to make at least one roster move to fill the spot. Melvin said it's unlikely Rich Hill, whose turn it would've been in the rotation, will be ready to start Sunday as he recovers from a nagging blister on his left middle finger.
"I don't see that happening at this point," Melvin said. "We'll have to do something different."
Alcantara worked with A's assistant Ron Washington on individual fielding drills prior to Wednesday's game, and he has already proven to be opportunistic this year, impressing coaches and hitting well at Triple-A, with a .296 average with Nashville.
Washington said Alcantara appeared comfortable despite a limited role.
"He's a very athletic guy. He loves playing the game," Washington said.
"What I'm trying to get him to understand is how to use his hands. When you're young, your mind makes you work a little quicker than you should. I'm trying to get him to slow down, because he has all the ability. He has range, good hands, an arm. I'm just trying to get him some reps that will make him all of a sudden smooth things out a little bit."
Mark Chiarelli is a reporter for MLB.com based in the Bay Area. This story was not subject to the approval of Major League Baseball or its clubs.