General manager Paul Holmgren stated the injury is a compression fracture and will require four-to-five weeks of recovery time.
Timonen's injury is the bookend to a brutal season for Flyers defenders. With the exception of Kurtis Foster, every defensemen who played in the Flyers' opening game of the season has missed at least one game due to injury. In total, Flyers defensemen have missed 115 man games out of 234 games lost this season (that number includes the 45 contests missed by Chris Pronger).
Considering Timonen's penchant for pain tolerance, it wouldn't be out of the realm of possibility that he has been dealing with the injury for some time. Earlier this season he was seen walking around the team's practice facility in a walking boot. Of course, the Flyers haven't confirmed when this injury occurred, so it's merely speculation.
Timonen played in 45 games this season and recorded 29 points (five goals and 24 assists). His 24 assists are ranked fourth-most amongst all defensemen in the NHL, as are his 29 points. In addition, the 38-year-old averaged 21:45 of ice-time per game, which included 3:48 on the power play and 2:55 on the penalty kill.
He signed a one-year, $6 million extension earlier this year, which will keep him under contract through the 2013-14 season.