Lowry had planned to throw off the mound on Monday for the first time since his surgery six weeks ago, but scrapped that plan in favor of the exam.
Manager Bruce Bochy declined to call it a setback and said he expected Lowry to throw on Tuesday, although he didn't know if it would be off the mound.
Lowry had surgery on his left forearm on March 7. The Giants had hoped he would be back in the rotation by the end of April, but Bochy said he would proceed with caution.
Lowry was 14-8 last season, leading the Giants in victories.