"There's a chance he'll be ready by Sunday," said manager Bob Melvin.
That's the earliest date Callaspo is eligible to return, after hitting the disabled list July 12 with a right hamstring strain.
The A's infielder is already taking part in all baseball activity and could be sent out for a short rehab stint at week's end. When he does return, the A's could choose to option Eric Sogard to Triple-A Sacramento.
Sogard has been with the club since the start of 2013 but made just his fourth start of the month Wednesday. He's hitting .194 on the season, though he did collect a pair of hits in Sunday's win over the Orioles.
"That was a key game for him," said Melvin. "We'd like to see him back it up."
Jane Lee is a reporter for MLB.com. Aaron Leibowitz is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.