The 26-year-old underwent surgery earlier this year to repair a fractured metatarsal, while the procedure also re-positioned another bone in order to protect the injured area.
"X-ray and CT scan studies done Thursday in New York reveal no fractures or bone injuries," Nets medical director Dr Riley Williams II said in a statement.
"Brook has been diagnosed with a mild midfoot sprain and is likely to be out for approximately 10-14 days."
Lopez has averaged 18 points, 5.6 rebounds and 54.2% shooting in 23.3 minutes per game in three pre-season outings, but he now faces another spell on the sidelines.
The Nets star also underwent surgery in March to repair a torn tendon and to tighten lateral ligaments in his left ankle.