"He could be out a while," Del Negro said after Monday morning's shootaround. "A week, two weeks, a month. I don't know yet.
"It's going to be how he reacts. How his foot reacts. When you get him back, his conditioning and his minutes [have to be considered]. It's not the perfect scenario."
The Bulls have tried different treatments to get Noah back on the floor.
"They're doing everything," Del Negro said. "Every technology that's out there.
"[Bulls physician] Dr. Cole is very smart, does a great job. Is very thorough. They've done a great job with everything they've done for Jo. Now it comes down to rest and continually getting his treatments. And see how he reacts."
Del Negro, who dealt with plantar fasciitis a couple times during his playing career, knows how fickle the injury can be.
"Sometimes you can rest for a week or two weeks and it feels pretty good, and you go out there and the first time you turn or something it hurts it again and you're out," he said. "Sometimes you rest it and it just goes away. Whether it's different insoles or sneakers or whatever. It's really hard to get rid of."
Nick Friedell covers the Bulls for ESPNChicago.com.