He'll pitch one inning, then start again for Sacramento on Friday and pitch an inning or two.
On Monday, Calero said he was expecting to pitch again in Sacramento on Saturday to see how his elbow responds to working consecutive days. A's manager Ken Macha, however, said he'd like to have Calero back by Saturday.
The two weren't quite on the same page Tuesday, either.
"I think they want me to pitch [in Oakland] on Sunday," Calero said.
"In all likelihood," Macha said, "he'll pitch [in Sacramento] Friday and be available [to the A's] Saturday."
Whenever he comes back, Calero will do so with something of a new weapon. Primarily a fastball-slider guy, he plans to start throwing more changeups.
"I've always had it, but I haven't used it very much because I didn't need it," he explained. "When I was in St. Louis, [Cardinals pitching coach Dave] Duncan used to tell me, 'You should throw your changeup more. It's a good pitch for you.' But I only threw it once in a while, just to show it.
"Now, I'm going to start throwing it more. It gives the hitter one more thing to think about."
Oakland's athletic trainer, Larry Davis, has said that Calero's slider -- he throws it at two different speeds, creating two different breaks -- might have caused the tendinitis, but Calero said he has no reservations about throwing it.
"I was dropping my arm angle a little when I was throwing it, and that might have caused some trouble," Calero conceded. "So I brought my arm back up to where it needs to be, and it felt fine yesterday when I was throwing it. I have to throw that pitch. It's my out pitch.
"So whenever I need it, I'll let it go, no problem."
Dribblers ... Mark Kotsay got his first start in the No. 3 spot in the batting order, but Macha said the move was more about getting Marco Scutaro into the No. 2 hole. Macha liked what he saw out of Scutaro last week against Tampa Bay's Hideo Nomo, who started for the Rays on Tuesday. ... Switch-hitter Bobby Kielty, after striking out three times against Nomo from the left side of the plate last week, batted from the right side in his fourth at-bat of that game. Kielty said Nomo's deceptive delivery makes it hard to see the ball from the left side, so he stuck to batting from the right side on Tuesday. ... Davis said righty starter Rich Harden, on the DL with an oblique strain, might throw off a mound for the first time since May 14 late this week. There remains no timetable for Harden's return. "His progress hasn't been as rapid as we'd hoped," Macha said. ... Righty reliever Chad Bradford, who had back surgery this spring and is on the 60-day disabled list, will start throwing off a mound late next week in Arizona. Davis said an optimistic projection would have Bradford returning to the A's just after the All-Star break.
Coming up: Barry Zito (1-6, 4.85), for whom the A's have scored a total of three runs in his six losses, will make his 12th start of the year Wednesday in the series finale against the Devil Rays.