The highly touted Nakajima, 32, never played a major league game after receiving a $6.5 million, two-year contract in December 2012. He missed time in his first season of 2013 because of a strained left hamstring, and the A's didn't have the same need for a shortstop once they acquired Jed Lowrie from Houston in early February of 2013.
Nakajima, a seven-time Pacific League All-Star, becomes a free agent. He had a .302 batting average with 149 home runs, 664 RBIs and 134 stolen bases over 11 seasons with the Seibu Lions.
He batted .267 with 10 home runs and 69 RBIs in 175 games at Triple-A and Double-A the past two seasons.