Noel had been diagnosed with an inflamed plica while already nursing a groin strain.
The big man is eligible for a rookie-scale extension, but his inability to stay healthy makes the possibility of an agreement unlikely by the October 31 deadline.
From the Sixers:
During the normal course of evaluation and treatment for his left adductor strain, which was identified on October 6, Noel reported localized soreness in his left knee. After consulting with multiple specialists, the source of the soreness was identified as inflamed plica. Noel has elected to address the injury via a minor surgical procedure in the coming days.