Celtics center Robert Williams III will miss all of training camp and the preseason with left knee surgery he's expected to undergo this week days from the beginning of the NBA season with media day on Monday. Heavy's Sean Deveney and ESPN's Adrian Wojnarowski first reported the planned operation, as well as the expected 4-6 week timeline Williams III now faces.

The knee is the same he underwent a meniscus removal surgery on in March in an effort to get back to the floor as quickly as possible for the NBA Playoffs. He returned three weeks later, dealing with a bone bruise, pain, swelling and restricted movement that limited his minutes and effectiveness through the NBA Finals.

Now, a source told CLNS Media that the impending surgery is to address a small tear in Williams III's left knee in what's being described as a cleanup arthroscopic, or minimally invasive, procedure. It's unclear if the procedure is related to the initial procedure from March or the postseason run that followed, which wasn't supposed to put Williams III at risk long-term.