Stewart has been on the disabled list since June 13, and sought a second opinion from a specialist June 18 at the Cleveland Clinic.
Asked if the third baseman would need surgery, Cubs general manager Jed Hoyer said Saturday: "It's a strong likelihood."
Stewart was batting .201 with five home runs and 17 RBIs in 55 games with the Cubs.
"They haven't made a complete decision," Cubs manager Dale Sveum said about the possibility of surgery. "There's some calcification on the bone that's causing some of the problem."
A decision was expected around the All-Star break.
"We're probably going to have to make that decision pretty soon," Sveum said. "There's no progress going on, so we'll have to make that decision."
Said Hoyer: "It's been frustrating for Ian and frustrating for us."