Strickland writes that McDonald had five documented concussions over the course of his career. Apparently, the threat of long-term brain damage has been a concern of McDonald's for some time. Following the team's elimination from the Stanley Cup playoffs, he and his family determined that retirement was the best course of action.
The fear of the next potential concussion was the catalyst for McDonald's decision, via True Hockey:
"The last few years too much of the focus became worrying about the next hit. I was always thinking about it.
"I'm fortunate to get out now. I know I could play two or three more years and I love the game of hockey, but healthwise I know I shouldn't be playing."
According to a report by the St. Louis Post-Dispatch, McDonald had considered retiring prior to the start of this season due to concussion issues. Ultimately, he decided to play this season. The 35-year-old forward completed the final year of a four-year, $18.8 million contract in 2013 and was scheduled to become an unrestricted free agent this summer.
In 685 career regular season games in the NHL, McDonald collected 489 points (182 goals, 307 assists). In 2007, he won the Stanley Cup as a member of the Anaheim Ducks.