Any injury that's hampering a player to THIS degree would be something the player would sit out for at some point. It's either a minor injury that he can work through, in which case he should be looking better than he is, or it's a serious enough injury that it renders you practically lifeless on the ice, and therefore something that he probably shouldn't be playing through.
You're right that both can be true, and I've already said that I can see there potentially be something nagging him, but most people agree this is mostly mental. If it was mostly physical or even 50/50 you can be sure the team would be more outwardly proactive.
Most people might agree, and I might even join them, but it's worth pointing out that none of us actually know much of anything. What bothers me about this whole Pettersson discussion, and actually a lot of discussion in general, is how we can so quickly move from educated guesses, to repetition of those educated guesses, to fact. The fact is, we don't know what's wrong with him. We do know, because he told us, that he has a knee issue that began at the exact time his production dropped. We do know, because he told us, that that injury hasn't gone away. And we speculate - speculate - that that or other issues have affected him mentally, to the point where he can't play effectively and "fight through it" in a way that is satisfying to watch.
Look, you seem pretty reasonable, so this isn't even really directed at you. I just hate the many examples of mind-reading, body language analyses, uninformed speculation, and various other forms of bullshit that surround this story, both on here and especially on other forms of social media. People really can't tell nonsense from fact, or maybe they don't even care to tell. Again, not directed at you, but it just drives me nuts.