McCarthy has been dealing with pain in his throwing shoulder, which has been pretty common throughout the pitcher's career. He spent the last two weeks of May on the disabled list and missed two starts only to hurt the shoulder again.
After firing seven scoreless innings Tuesday in his return against the Dodgers, the assumption was he'd be ready to pitch on five days' rest. The A's announced Saturday that will not be the case.
"For whatever reason, it just doesn't recover the way it's supposed to, or in time," said McCarthy, who fears another DL stint. "The soreness stays there longer than it should, the inflammation. I guess this is just another one of those times where that's the case."
The team did not announce a starter Saturday night. It's believed that A.J. Griffin, who is scheduled to start in Triple-A Sacramento and is 3-2 with a 2.81 ERA, will get the call.
Whomever the pitcher is, he'll be opposed by Giants starter Matt Cain, who enters the game riding an eight-game winning streak, which includes five starts allowing one or zero runs as well as the 22nd perfect game in Major League history. The streak has pushed his record to 9-2 on the year with a 2.34 ERA.
The right-hander has made nine starts in his career against the A's and is 3-5. However, a 2.19 career ERA vs. Oakland suggests his offense has let him down in those starts.
After throwing the perfect game on June 13, Cain followed it by allowing 10 baserunners and three earned runs in his last start Tuesday against the Angels. Manager Bruce Bochy called it a "gutty effort" by his starter, especially after throwing a season-high 125 pitches in the perfecto.
"He wasn't quite on, which is not surprising with everything he put into the last game," Bochy said. "He worked pretty hard in that game. He found a way to get it done. He just keeps grinding."
Giants: Belt riding 11-game hitting streak
After batting .203 in May, Brandon Belt has rebounded in June to hit .360 (18-for-50) with four home runs and 15 RBIs. He is currently in the midst of an 11-game hitting streak.
"The best way I can explain is that I found my swing," Belt said. "Earlier in the year, it was a struggle for me to find my swing for some reason. But you have to keep working through it, and I did, and I finally found my swing."
Pablo Sandoval is hitting .292 with one extra-base hit and four RBIs since his return from the disabled list June 9.
Athletics: Anderson throws off mound
A's right-hander Brett Anderson threw off a mound for the first time Saturday since experiencing a minor setback a month ago during his recovery from Tommy John surgery. Anderson threw 20 fastballs in his bullpen session and manager Bob Melvin was impressed.
"It was quick, it was efficient, the command was there," Melvin said. "Once he felt a little something, we wanted to take a step back because he was on such a progression, but every time I've seen him throw, he's been terrific. It looks like a guy just throwing a bullpen. Good first start getting back on the mound again."
The A's have used a league-high 15 rookies this season and Saturday, they called up Brandon Hicks from Triple-A Sacramento to replace Collin Cowgill, who left Friday night's game with a sprained left ankle and was placed on the 15-day disabled list. Hicks was hiiting .272 with 13 home runs with the River Cats.
"I'm hoping to carry some of that over," said Hicks, who hit a two-run double in the A's four-run ninth Saturday. "I got hot there on that last homestand. It was nice to hit some balls out of the park, and hopefully I can carry that over."
The A's look to leave Interleague Play with a positive record. With their 9-8 loss Saturday night, they are now 9-8 against the National League this season. The Giants are 7-7 against the American League.