"There's no need to rush him back," said Theo Epstein, president of baseball operations. "Let him heal and put him in a position to be 100 percent so he can have a big year next year for the Cubs."
Garza last pitched on July 21, and left that game with cramping in his right triceps. He was diagnosed with the stress reaction on Aug. 6.
Manager Dale Sveum said on Tuesday that he would be surprised if Garza returns. The right-hander has not been allowed to pick up a baseball since the diagnosis.
"It'll be kind of tough," Sveum said about Garza coming back. "Some guys heal quicker than others."
Garza was 5-7 in 18 starts, with a 3.91 ERA.
"In his mind, he wants to come back and pitch," Sveum said.