According to CSN Washington (I’m watching the Caps game), he did have a problem with blood clots associated with long plane rides in his recent past - from a user on Kulka.inferno31 wroteCOLONPulmonary Embolism. Rare in athletes to say the least. Possible causes: Long term immobilization (trans atlantic flight, bed rest), recent surgery, bone break, or hes got a genetic defect. I think the long term immobilization isn't likely even though its the most common cause, but I don't know if hes had a recent surgery or a bone break. The doctor said he'll be on blood thinners for the rest of the season, so that could be bone break or recent surgery.
I was talking about this with a friend, it could possibly be blood doping. No one wants to discuss the elephant in the room, but Pulmonary embolisms are a side effect of it for sure, and even though hes with the avs now the caps organization had some questions around it.
So looks like thats the cause.