Guzman's choices are to either elect to have surgery or try to build the muscles around the tear and continue to pitch.
An MRI on Friday revealed the tear. Guzman had a related injury under his armpit last September when he had to be shut down.
Sources said that the two injuries are related. Meanwhile, the Cubs will pursue bullpen help elsewhere as general manager Jim Hendry will have his scouts looking for veteran bullpen help, just as he's done over the last 10 weeks.
"You just feel terrible for the kid," Hendry said. "He's had such a history ... right when he's had success, something has gone wrong."
It's been a sad offseason for Guzman, whose brother, Daniel, died in his arms two months ago after being shot in their native Venezuela. Five days earlier, Guzman had sustained a knee injury that required arthroscopic surgery.
He began to complain of shoulder pain last month. Every time he thought he was recovering, he had a setback, and he finally underwent an MRI on Friday.
"It's a shame," Piniella said. "It seems like the kid is jinxed."
Hendry said Guzman probably will work on strengthening his shoulder for the next four to six weeks. If that's successful, he could start throwing again. Surgery would be a last resort because the required procedure would be invasive and wouldn't guarantee a full recovery.
Guzman was expected to battle for the right-handed setup man role, which would complement closer Carlos Marmol and left-handed setup man John Grabow. The 28-year-old Guzman appeared in 55 games last season, going 3-3 with a 2.95 ERA.
Information from the Associated Press was used in this report.