Near the end of the second period of Wednesday night's game, Cooke and Karlsson chased down a puck in the Ottawa defensive zone. After Cooke engaged Karlsson, his foot left the ice and came down on the back of Karlsson's left leg just above the backing of his skate.
The result was a lacerated Achilles Tendon for Karlsson, which will require surgery. He will be out for an indefinite period of time.
Addressing the incident, the Senators expressed their displeasure and referenced Cooke's checkered past when explaining how they view the intent behind the unfortunate injury.
The NHL has contacted both teams' general managers to inform them that supplemental discipline will not be used in this instance.
The injury to Karlsson is another addition to a growing list of Senators key players forced out the lineup due to injury. Forward Jason Spezza is expected to miss most of the year due to an upper-body injury and Milan Michalek was unable to play in Wednesday night's game due to a lower-body injury.