Parker, 24, started Saturday's game and was working a shutout against the Cardinals, but felt tightness in his hamstring while pitching in the fourth inning. Manager Bob Melvin and an Athletics trainer came out to look at him. After a few warmup pitches, the decision was made to remove Parker from the game when he said he could still feel discomfort.
The team is hoping Parker was only suffering from a cramp. If that is the case, Parker would likely be able to make his next scheduled start on Thursday or Friday.
Parker has been pitching very well since late April. After posting an 8.10 ERA through his first five starts, Parker has since recorded a 2.91 ERA and .622 opponent OPS over 12 starts. Before he was removed from Saturday's game, Parker had a streak of nine consecutive quality starts.