Everyone gets really touchy about this, and that's a part of the problem. Such a suggestion seems to amount to all a full blown character assault. This is why many suffer silently with addiction. Without that stigma we could address it as we do any other ongoing injury or ailment, quickly and more effectively.
This is not to suggest Matthews is, without any doubt, dealing with substance abuse issues. But he is human, fallible, and in a position that grants him all access and every excuse one would need to partake. He's the face of the biggest franchise in the NHL, is well regarded by the opposite sex, and hangs out with a celebrity who has a long history of drug abuse issues.
His overall play last year was baffling to me. I tried to think of anything that could be causing a guy who was once one of the strongest players on his skates in the league to end up on his ass constantly. To regularly fumble the puck with no pressure on him. To look as gassed as Phil Kessel after a short shift.
It looked like a concussion, but he hadn't had an injury to his head in ages. Then I'd see him talk in pressers and he looked exhausted, eye bags deeper than I'd ever seen them, pale, and generally unwell. That's when I started to quietly suspect what it might be. Now I've heard from someone who knew him intimately that he does, in fact, have more than a passing fondness for that lifestyle.