Overall, this is because Landeskog has been dealing with a gnarly injury to his right knee. It is one of those injuries that is hard to shake and it has required some pretty significant surgeries. For instance, he got a cartilage transplant, which typically would spell the end of someone's career.
However, Landeskog is a fighter and he is promising fans that he will come back strong. Corey Masisak of the Denver Post reported that Landeskog confirmed he will return this season. Although, it still remains to be seen when the exact date will be.
Once again, there are no guarantees right now. At the end of the day, Landeskog will simply have to do things at his own pace. Hopefully, he can get back to where he used to be, sooner rather than later.