Forst said Major League Baseball "pushed the issue, asked the insurance carrier to make an exception to allow him to pitch, and they didn't do it."
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"It's an unfortunate thing, but at the same time it allows me to slow down here and get myself as ready as I can in camp for the beginning of the season," said Gray, who was sidelined by a trapezius strain and then a forearm strain in 2016. "As much as I would have liked to participate and represent the A's and Team USA, there's nothing you can really do other than try to get ready for the season."
With Gray unable to suit up for Team USA, the A's have adjusted his spring schedule, pushing his first Cactus League start to Wednesday against the Padres. He was originally penciled in for a Monday start in opposition of the Giants.
Others were affected too: right-hander Kendall Graveman's first start was switched from Sunday to Monday, opening up a start for No. 7 prospect Daniel Gossett in Sunday's home opener against the Angels.
"We were trying to rush [Gray] a little bit to get him on schedule for that, and in turn, it affected Kendall, too, so the prudent thing to do is give Kendall an extra day and get Sonny back on his regular turn," A's manager Bob Melvin said. "Overall, this works out better for them with us, but I know Sonny's disappointed because he really wanted to pitch in the WBC."
"There are different rules in place, and it just didn't work out for me," Gray said. "I would've had a great time, and I would've enjoyed going along and try to compete on a larger scale in spring, but at the same time, it does allow me to get back on track and get a couple more days here and do everything I can to get myself ready to make myself the best pitcher and perform for the A's the best I can."
Gray, who was going to latch on with Team USA in the second round, joins Russell Martin as the second player to be deprived of World Baseball Classic participation because of insurance issues -- and he is the third A's player to cancel Classic plans, with outfielder Khris Davis (Mexico) and reliever Liam Hendriks (Australia) opting out of the tournament.
Pitchers John Axford (Canada) and Santiago Casilla (Dominican Republic) are still participating.
"I know it didn't work out," Gray said, "but just to have the chance to do it and be asked to play is very humbling. Maybe in the future it's something that can work out."