Jackson was removed from Saturday's game against Arizona with an apparent injury, Maria I. Guardado of MLB.com reports.
Jackson immediately signaled toward the Giants' dugout to come get him after throwing a pitch in the sixth inning. The 31-year-old reliever missed two months at the beginning of the season while recovering from Tommy John surgery. The Giants will take a look at him and provide further updates in the near future, but the fact Jackson immediately knew something was wrong is not a positive sign.