MacArthur played the first four games of the season before missing the rest of the season with a concussion. He suffered a concussion last season, but returned to play in the playoffs. He seemed to suffer another concussion in the pre-season, but came back to play when the season started. He was trying to come back in early March, but failed his baseline test. He passed his most recent baseline test, making him medically able to play, but with the Sens missing the playoffs this year, there was little reason to risk the long-term health of one of the team's best left wings.
Phaneuf had a sore foot after blocking a shot on March 12. Initial x-rays came back negative, but further testing revealed a hairline fracture. It seems likely that if the Sens were pushing for a playoff spot, the February acquisition would be playing. Instead, he will have a chance to heal fully before starting his offseason training.