Per ESPN's Pierre Lebrun:
No hearing for Cooke, no Supplemental Discipline. Shanahan spoke with both GMs.
It's the right call, and just an all-around unforunate play. Matt Cooke and Erik Karlsson were racing for a loose puck, Cooke was trying to get position to pin the defenseman to the boards, and unforunately something bad happened.
Murray's response is easy to understand; he's an emotional guy and his team was just dealt a devastating loss of their best player. As Penguin fans, we know how bad that feels seeing your top player get hurt like that.
As for Neil, it's his job to do what he did, but it's not going to change anything or make Karlsson's leg better. Some fans have cried that Cooke ducked Neil, but the play was an accident and Cooke didn't "owe" the Senators anything. Cooke has answered the bell in the past- he took his medicine from Shawn Thornton in 2010 after the Marc Savard hit, and he also fought the first guy who challenged him, Ryan Callahan, after a bad hit on Artem Anisimov. Cooke will give a fight when necessary, but this was not a case of that since it wasn't more than an accident on a hockey play.
This isn't to defend what Cooke has done in the past, his dirty play stands on its own. For a player who will drop the gloves to answer himself when he knows he did wrong, that Cooke didn't is another signal that nothing he did was intentional.
What adds insult to injury is that this play shouldn't have happened- seconds before Cooke and Karlsson went into the corner, the puck had gone off the netting, which should have had play whistled dead. The Root Sports broadcast picked this up and mentioned it, but the referees missed it and the ill-fated play happened. It's a shame that a weird injury happened to a star player in such a manner. Here's to hoping for a quick recovery.