Garza said his goal is to get back on the mound this season, despite there being no official timetable on his return.
"I'm hoping," Garza said. "That's why I'm working my tail off. Doing everything I can."
Garza hasn't pitched since he left his July 21 outing after three innings because of cramping in his right triceps. He threw a bullpen session Saturday in Los Angeles, but his arm was stiff Sunday and he returned to Chicago to be examined. The results were discovered Monday.
The 28-year-old right-hander said he was surprised at the diagnosis of the injury, which he originally thought was just a sore muscle.
"I was throwing through this thing. I thought it was just another slow bump, I'd be fine and keep going," Garza said. "But the doctor said that we've got to shut it down, and you've got to listen to the doc."
Garza won't be allowed to pick up a baseball for the next two weeks. He admitted he hasn't been in the best of moods because of that, which was evident to Cubs manager Dale Sveum when he saw him Thursday afternoon.
"He wasn't in the typical Matt Garza spirits, that's for sure," Sveum said.
Garza didn't try to hide his disappointment.
"It [stinks]," Garza said. "They're not letting me throw a ball. That's what I get paid to do, so it's not fun to come here and sit down.
"Yeah, I get to work out and ride a bike and watch a ballgame, but it's still not what I like doing. I like being out there taking control of the game and being able to do what I get paid to do."