The 29-year-old McCarthy underwent two hours of surgery late Wednesday to relieve pressure on the brain after the ball hit the right side of his head. He experienced an epidural hemorrhage, brain contusion and skull fracture on the play off the bat of the Angels' Erick Aybar.
McCarthy, Oakland's opening day starter, is 8-6 with a 3.24 ERA this year in his sixth big league season and second with the A's. He went 9-9 with a 3.32 ERA last season.
McCarthy joked Saturday: "The good news in all of this, is that I set up my fantasy lineups beforehand. So there shall be no excuses at this point."
Earlier, he made a funny reference to how "crazy" he is for the children's pain medication he gets -- and "can't believe they give it to kids." In response to a get-well greeting from 49ers All-Pro linebacker Patrick Willis, McCarthy quipped, "Thanks, buddy, I feel like I just got hit by you."
His lighthearted posts came a day after trainer Nick Paparesta said in Seattle that McCarthy was still in a "life-threatening" situation. Paparesta said Saturday at Safeco Field that the pitcher had been examined by a neurosurgeon earlier in the day and is progressing nicely. McCarthy was able to ask his own questions to doctors about his condition, too.
McCarthy is recovering in a Bay Area hospital, and might soon be moved to a transitional care unit in the building that is one step closer to a regular hospital room.
Paparesta said the first few days after a traumatic head injury are crucial.
"I'd give him one more day. I think with any head injury, you need to be cautious, and that's where we are," he said. "There is caution there. But the progress has been great and we're all very excited about it."
His wife, Amanda, also has been regularly posting on Twitter as usual.
When asked about McCarthy's Twitter posts, Paparesta was encouraged.
"I think that that's great. As you can tell they are his thoughts, and that's important," Paparesta said. "People are able to see that he's still got it all together."
Before the Dodgers-Giants afternoon game at AT&T Park, players in both clubhouses were eager to hear updates about McCarthy's progress.
"That scares me so much," Giants manager Bruce Bochy said while seeking an update on McCarthy's injury.
Paparesta said McCarthy's long-term health and wellbeing -- not his baseball career -- is the priority.
Everyone is concerned.
"Oh yeah, guys talk about it to see what happens," Los Angeles manager Don Mattingly said. "It kind of reminds you just how dangerous, what can happen and how fast it can happen. It puts it in perspective of what you're doing."
Dodgers second baseman Mark Ellis played with McCarthy for part of 2011 with the A's before being traded to Colorado. While Ellis said it's always good to see someone get up from such a frightening moment, that doesn't always mean everything is OK.
"It's especially hard when you played with a guy to see something like that," Ellis said. "You're happy to see him get up, but I'm so glad they did all the tests to make sure."
AP freelance writer Bob Sherwin in Seattle contributed to this story.