While the news isn't quite as good as hoped, it's certainly not as bad as it was feared. After suffering a knee injury in his very first training session with Napoli after joining the team on Wednesday, Alberto Grassi has undergone surgery to repair the damage and is expected to be out for three weeks.
Grassi suffered an "acute traumatic injury" to the medial meniscus in his right knee. Not one of the ligaments in the knee, the meniscus acts as a sort of shock absorber in the knee, helping prevent contact between the tibia and fibula, and when torn it can cause significant swelling through fluid buildup, instability in the joint, and quite a bit of pain and discomfort. The surgery would have been to remove any detached or partially torn material from the meniscus, and to make sure there was no additional damage.
While that sounds bad, it's actually a relatively minor injury, though more serious than the minor knee sprain many were hoping for after some optimistic reports in the hours following Grassi's injury. It's also significantly less serious than an "acute traumatic injury" would have been if it had involved his ligaments, as Lorenzo Insigne can attest to.
The three week timeline given by Napoli's medical staff is fairly standard for a meniscus operation, though it will still be reliant on Grassi's recovery and rehab going well. There shouldn't be any complications from this type of surgery, but as Camilo Zuniga would tell you, the knee is a very tricky thing. Here's to hoping for the best for Grassi, and also hoping that we'll see him make his Napoli debut sooner rather than later.