Today, we learn that this upper body injury is indeed a rib injury, as reported by Maxime Truman on BPM Sports.
Let's bet that Jonathan will try to come back to the game as soon as possible, he really needs a convincing season for his future in the NHL, but knowing that it's a rib injury, you have to know that it can take a long time to heal completely. (and in the meantime, it's painful)
The "good news" if you can call it that, is that his current upper body injury is finally not related to his wrists, contrary to some rumors.