Thomas, 24, was the son of A’s pro scout Tom Thomas.
Vice president of baseball operations Billy Beane expressed the emotions of the organization in a press release put out by the team Tuesday:
“We were devastated to hear of this tragedy within the A’s family. Our hearts go out to Tom and his family on their loss; Casey was a wonderful young man and teammate, and will be missed by all in the A’s organization.”
Oakland selected Thomas, a Kansas City native, out of Texas A&M-Corpus Christi.
At the time of his death, Thomas had been participating in extended spring training. No further information regarding cause of death was available as of early Tuesday afternoon.