CHICAGO -- A key contributor won't be in the lineup for the Chicago Bulls when they tip off against Houston on Saturday.

Swingman Otto Porter Jr. has been ruled out against the Rockets with a left foot sprain, with no timetable for his return.

"It's a soft-tissue injury, so it's something that's difficult to put a timetable on," Bulls coach Jim Boylen said during Friday's practice. "That's about as easy as I could say. We're not exactly sure.

"I don't want to give you a definite timetable because it could be sooner or longer than maybe we see," he added. "I know that's vague and I'm sorry for that, but that's the kind of injury it is."

Porter suffered the injury during Wednesday's victory at Atlanta after a hot start with 13 points, 4 rebounds, 2 assists and 2 steals in 12 minutes.

For the season, the Georgetown product is averaging 11.2 points on 41.7% shooting as the team's fourth-leading scorer. Chandler Hutchison is expected to start in Porter's place against the Rockets.

"Because of the soft tissue, these are things that maybe it settles down in 24 to 48 hours," Boylen said. "Maybe it doesn't. That's where the uncertainty comes in where it's difficult to put a timetable on. So yes, it did not settle down like maybe we had hoped other injuries have. We're not taking any chances with him, or anybody. We'll manage him accordingly and support him in the appropriate way."