Hahn played catch in Anaheim on Monday, and the blister "looks better," according to A's manager Bob Melvin, but the club does not want to rush Hahn's return.
"Jesse Chavez is a good guy to have in your pocket when something like that happens," said Melvin.
It's not yet known when Hahn will make his next start, since the A's could potentially use their April 27 off-day to alter their rotation.
• Right-hander Jarrod Parker on Thursday will take the mound in a game for the first time since undergoing Tommy John surgery last spring. Parker is scheduled to start for Class A Advanced Stockton in Visalia and throw four innings.
Jane Lee is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.