Sonny Gray became the third A’s player to step back from the World Baseball Classic in a week, but his departure from Team USA was not Gray’s choice. “As much as I’d like to participate and represent the A’s and Team USA, it’s just an unfortunate thing that came up and there’s nothing we can really do except try to get ready to start the season,” Gray said Sunday at Hohokam Stadium. The A’s ace wanted to pitch in the second round of the WBC next month, but the insurance carrier for the event pulled the plug because Gray didn’t meet some requirements after twice missing time with injuries last year. Gray spent more than 60 days on the DL, he was on the DL in late August and when he returned, he didn’t pitch more than 10 innings. “It’s not up to us or MLB, it’s up to the insurance company,” A’s general manager David Forst said. Canada’s Russell Martin also was denied insurance coverage for the WBC this season because of a previous knee injury. With Gray unable to participate in the WBC, the A’s shifted him from a scheduled start Monday against the Giants to Wednesday at the Padres, slowing things down for him. Kendall Graveman was moved from Sunday’s home opener to Monday at the Giants, with Sean Manaea still scheduled to work second, and minor-league Daniel Gossett wound up getting the start Sunday vs.