The team announced the injury in the third inning.
Hahn pitched just two innings in the game against the Marlins, giving up five runs on seven hits while striking out two. He gave up a single to Christian Yelich in the third then left after a visit to the mound by the Oakland trainer. He entered the game 1-3 with a 3.18 ERA.
Hahn said afterward that his arm tightened up in the third but he never felt any discomfort. He wasn’t sure if he would undergo an MRI on Wednesday, and was also unsure if he would make his next start.
The A’s also lost first baseman Yonder Alonso to injury when he left in the seventh inning after being hit on the right wrist by a pitch.
X-rays were negative, and Alonso said he would see how the wrist feels overnight and in the morning before informing A’s manager Bob Melvin of his status for Wednesday’s game.