The 32-year-old defenseman sustained the injury during an offseason workout and will be out approximately six weeks, according to the Flyers.
MacDonald had 21 points (six goals, 15 assists) in 66 regular-season games with the Flyers last season and two goals in six Stanley Cup Playoff games. His 19:51 average ice time per game ranked fifth on the team.
Training camp begins Friday for the Flyers. Their regular-season opener is Oct. 4 at the Vegas Golden Knights.
In 11 NHL seasons, MacDonald has 152 points (28 goals, 124 assists) in 529 regular-season games with the New York Islanders and Philadelphia Flyers, and five points (four goals, one assist) in 23 playoff games.