It will be his first in the Majors since June 19, after dealing with the same right shoulder soreness that has plagued much of his career.
Though he was missed, the A's have done just fine without him, moving from four games under .500 (32-36) at the time of his setback to eight above it (59-51) entering Wednesday.
When healthy, McCarthy is one of the league's best, having compiled a 2.54 ERA in 12 starts for the A's this year. The club's Opening Day starter completed at least six innings in all but two of those outings and has gotten through seven in seven outings.
When stepping to the mound Friday against the White Sox, one of his former clubs, the 29-year-old McCarthy will be expected to tally 80-90 pitches. He'll take the rotation spot of the injured A.J. Griffin,
"He's very efficient with his pitches," A's pitching coach Curt Young said of McCarthy. "That's the key to his game. He gets a lot of early outs and makes things happen quick."
McCarthy made two rehab stints with Triple-A Sacramento, his most recent coming Sunday, when he threw just 73 pitches despite striking out nine over six shutout innings, allowing just two hits and issuing two walks.
His return is welcome news for an already pitching-rich A's, who are also close to getting lefty Brett Anderson back. Anderson is slated to throw 90 pitches for the River Cats in Oklahoma City on Friday, before throwing 100 five days later, at which point the A's will assess his readiness for big league action.