Gray was at home with his family as of Wednesday afternoon and will likely return to the A's clubhouse on Thursday.
A's manager Bob Melvin is still not sure whether Gray will start against the Mariners on Sunday, and he said Chris Bassitt will fill in again if Gray remains sidelined.
Though the sickness is contagious, no other members of the A's or Gray's family have taken ill. A's manager Bob Melvin said Chris Bassitt will pitch Sunday against the Mariners if Gray does not.
"He's getting much better, no fever," A's team physician Allan Pont said. "He's rounding into shape."
Pont said it's the first time in 32 years working with the club that he's sent someone with gastroenteritis to the hospital.
Gastroenteritis is typically brief and doesn't necessarily lead to a high fever, Pont said, but Gray has had a high fever and severe intestinal problems for multiple days.
"It's been a bit of a roller coaster for him," Melvin said. "Just when he started feeling good, then he wouldn't for a period of time. He's been there for a couple days."
Pont said you can treat gastroenteritis without antibiotics, but he and his colleagues prescribed antibiotics for Gray because of the severity of the situation. At first, the treatment was simply to drink lots of water, but as the sickness intensified so did the treatment.
Pont said he and his colleagues have looked extensively for a cause, but have yet to identify one. Pont is just relieved the sickness didn't make its way to the A's locker room.
"If it were the clubhouse, I'd probably be playing today rather than the players, because everybody else would be out," Pont said.
He added that any weight loss won't be significant, as Gray shouldn't lose more than a pound or two. Gray should be fine long term and back with the A's in the coming weeks, but it's now clear he was battling more than flu-like symptoms.
Said Melvin: "This wasn't a minor thing."