A CT scan after the accident showed McCarthy had an epidural hemorrhage, brain contusion and skull fracture. McCarthy was transferred to another hospital and had a second CT scan. He then underwent 2 hours of surgery Wednesday night to relieve pressure in his head.
A CT scan taken Thursday showed improvement from the previous scans and McCarthy is currently resting in the hospital.
The A's did not give a timetable for how long McCarthy will be out.
"Our first concern is Brandon's health, and we are heartened to learn he has shown progress in his recovery after surgery," general manager Billy Beane said. "We are glad to report he is stable, awake and alert. The team will provide further updates as they become available in the coming days . . . Brandon remains in everyone's thoughts as we wish him a speedy recovery."
The A's traveled Thursday to Seattle, where they will begin a three-game series on Friday against the Mariners. Oakland went into the day tied for the AL wild-card lead with Baltimore after being swept in a three-game series against the Angels.
McCarthy is 8-6 with a 3.24 ERA in 18 starts.
The A's also announced on Thursday that third baseman Brandon Inge was placed on the 15-day disabled list with a strained right shoulder. Inge will have season-ending surgery on the shoulder.
Angels ace Jered Weaver will miss his scheduled start Friday against visiting Detroit while recovering from tendinitis. Weaver (16-4) was struck by a liner from Seattle's Dustin Ackley during a 2-1 loss to the Mariners last Sunday. An MRI on Weaver's right shoulder revealed tendinitis apparently unrelated to the line drive.
In a game Thursday *
At Baltimore, Mark Reynolds hit two of the Orioles' season-high six home runs, and Baltimore climbed back into a first-place tie with the Yankees in the AL East by defeating New York, 10-6, before a euphoric sellout crowd at Camden Yards.
* At Kansas City, Michael Young's singled in the 10th inning scored Ian Kinsler and the Texas Rangers defeated the Royals, 5-4. Josh Hamilton and Adrian Beltre homered for Texas.