Info is slim at the moment, but the official word from the Jazz website is as follows:
After sustaining a left knee injury during today's practice at Zions Bank Basketball Center, Gobert underwent magnetic resonance imaging (MRI) this afternoon at University of Utah Health Care's Orthopaedic Center. Following the examination, Jazz physicians Dr. Travis Maak and Dr. David Petron determined that Gobert suffered a Grade II sprain of the medial collateral ligament (MCL) in his left knee.
No surgery is required and Gobert will be out indefinitely. Further updates will be provided when appropriate.
Amar's occupied at the moment but will probably update this later with his medical knowledge. Best guess is that Rudy will be out until January at the very earliest, and maybe longer.
So, if the last few sprains of the same severity are any indication, Rudy Gobert will be out 4-7 weeks and therefore 16-30 games.— Andy Larsen (@andyblarsen) December 2, 2015
The first personnel move will almost certainly be to recall Tibor Pleiss from the Idaho Stampede of the D-League. From there, we might see Trey Lyles or Trevor Booker in the starting lineup, as we did when Rudy was out a few games earlier in the season. In those scenarios, Derrick Favors would shift to center. If the Jazz want to keep Favors at power forward, starting Jeff Withey is also an option. But Rudy's been playing 34 minutes a game, so that time has to go somewhere between Booker, Lyles, Withey and Pleiss. My guess is that all of them will see court time.
With Dante Exum already out, we knew the Jazz would never reach their full potential this year. But a long-term Gobert injury could cost Utah the playoffs -- especially if the team plays as badly without him as they did last month. I'm not sure a trade to bolster the frontcourt and keep the team more competitive makes sense, for the same reasons that a trade for an Exum replacement at point guard hasn't happened. It's heartbreaking, but there's a real chance that 2015-16 will simply be a lost season now. But that might be better than mortgaging assets to try and maintain momentum this year.
More info later as we learn it, but for now, this just sucks. Get well soon, Rudy.