The A's were expecting big things from shortstop Hiroyuki Nakajima when they signed him to a two-year, $6.5 million contract in December as a free agent.
But he has not hit well in the spring, and on Sunday, the A's placed him on the 15-day disabled list with a strained hamstring.
Nakajima, 30, suffered the injury in a game against the Cleveland Indians on Tuesday.
He hit just .167 with one extra-base hit in 49 plate appearances during the spring.
Jed Lowrie will play shortstop for the A's in the early part of the season.
The A's also optioned lefty Pedro Figueroa and infielder Andy Parrino to Triple-A Sacramento.