It's not immediately clear how long he will be out, but if in fact he did sustain a concussion, he will have to undergo MLB mandated medical tests to clear him for a return to the field. With only a few weeks remaining in the regular season, his year could be in doubt.
The A's are second in the AL West and continue their series in Chicago on Wednesday.
Gentry has a concussion. — Susan Slusser (@susanslusser) September 10, 2014