The injury occurred during offseason training and Seidenberg has not participated in any training camp activities.
Seidenberg played the full 82 games for the Bs last season, scoring three goals and 11 assists.
The 34-year-old defender played just 34 games in the 2013-14 season, after being sidelined with a knee injury.
The eight week timeframe puts Seidenberg’s return, if all goes well, at the second week of November, meaning he’ll miss slightly more than a month of regular season play.
This is the team’s second injury this preseason, with news coming earlier this week that Seth Griffith will miss three to four weeks.