"It was a 24-hour bug that a lot of guys have gotten," Gray said Tuesday before the A's faced the White Sox at the Coliseum, "and I just so happened to get it on the wrong day."
Gray was back in the A's clubhouse on Tuesday, and he has been given the green light to make his season debut Wednesday with a start against the White Sox.
"As you can see," he said, "there are a lot more hand sanitizers around the locker room today."
Graveman is currently Thursday's scheduled starter, and A's manager Bob Melvin said, "From what I understand, he's going to be able to start on Thursday, but had a little bit of a tough night last night."
Melvin gathered his squad for a team meeting with head trainer Nick Paparesta on Tuesday afternoon to discuss ways to combat the virus.
"I've had this Purell dispenser in here for years," Melvin said, smiling, "and now everybody doesn't think I'm so crazy."
Gray said he lobbied to pitch Monday night but ultimately understood the team's decision to postpone his start. Left-hander Rich Hill, originally scheduled to start on Tuesday, stepped in on short notice and allowed four runs in 2 2/3 innings of a 4-3 loss.
"I was upset and unhappy, and a lot of people can say they were, but I can guarantee they weren't more upset than I was," Gray said. "In the grand scheme of it, it was one game and I'll be able to take the mound tomorrow. I'm pretty excited to get out there tomorrow."
Jane Lee is a reporter for MLB.com. Follow her on Twitter @JaneMLB. This story was not subject to the approval of Major League Baseball or its clubs.