The A's ventured across the Bay Bridge for the first game of the series on Thursday, and it was during that time that Nakajima was scheduled to be seen by the team's doctors to determine the next course of action.
Doctors confirmed the strain but offered no indication of how much time he'll miss, making a DL stint all the more likely.
Uncertainty not only surrounds Nakajima's health, but his ability to compete in the big leagues. The Japanese shortstop struggled all spring, both on defense and at the plate, and his slow progression has cleared the way for Jed Lowrie to take over everyday shortstop duties.
The A's aren't yet ready to say as much, but there's no denying that his injury only adds to an already difficult adjustment period. For now, though, they're not ruling him out of playing in the first week of regular-season games.
"It's tough to say, it is," A's manager Bob Melvin said. "If he misses three games here and a couple back there, it would be difficult to get back into the swing of things, but I'm not really sure yet."