"He tried," manager Mike Redmond said. "He came in my office and he told me, 'Red, I can't do it. I just can't do it.' His thumb is all swollen, it's black and blue. I know he tried. Jose wanted him, too.
"I know Jeff really wanted that. I knew that was important for him to be back for Jose's last start. It's too bad."
The last time Mathis didn't catch Fernandez was on June 25. Rob Brantly caught that night against Minnesota. Koyie Hill was behind the plate Wednesday night.
"Koyie is a veteran guy too," Redmond said. "He will be fine."
Mathis injured his thumb in the fourth inning of Monday night's 5-2 loss to the Braves while trying to block a wild pitch in the dirt.
An X-ray that night came back negative. When the swelling subsides, a second X-ray will be taken to make sure there isn't a fracture.
"There will probably be another X-ray to rule out a fracture," Redmond said. "I think sometimes after the initial trauma to the finger, you let the swelling get out of there and re-evaluate. Hopefully everything is fine."