The Bruins' best player in the Stanley Cup playoffs, Bergeron suffered a mild concussion in Boston's Game 4, series-clinching victory over the Philadelphia Flyers. His absence clearly was a factor in the Bruins' Game 1 loss to the Tampa Bay Lightning on Saturday night at TD Garden.
Because he's so important in every aspect of Boston's game, the Bruins need Bergeron back to have success in this series. He has skated on his own the past two days, which is a good sign, but there's no way the team will rush him back even with a trip to the Stanley Cup finals at stake.
"If he's not 100 percent, he will never play," Bruins coach Claude Julien said. "And whether it's regular season or playoffs, our organization, even before [the NHL] tightened up the rules on that, there is no way we would ever do that to a player. That is too important to his personal lifestyle and the life he is going to lead after hockey. That will always come before the game.
"It's unfortunate, but that's the way it should be. And we believe in that and we are going to continue to enforce it. So the day you see Bergy back in our lineup, he will be 100 percent. If he's not, you're not going to see him."
Bergeron is the Bruins' top centerman and without him taking faceoffs, Tampa dominated in that category (41-26) in Game 1. He's also a cog on special teams for Boston.
While the Lightning are concentrating on their game, Tampa players also felt the absence of Bergeron.
"He's one of the best two-way players in the league," Tampa forward and former Bruin Nate Thompson said. "He's unbelievable at faceoffs, he penalty kills, he plays the power play, he does everything. That's a big hole in their lineup and we have to still prepare as if he's playing."
Even though they're opponents competing at the highest level, Thompson wishes Bergeron a speedy recovery.
"It tough and you never want to see that happen to a guy, especially a good guy like Bergy," Thompson said. "He plays the game the right way and it's tough luck. You don't want to see that happen to anyone in the game and I just hope he gets better."
With Bergeron sidelined, Julien decided to insert veteran forward Chris Kelly onto the Bruins' second line, along with Mark Recchi and Brad Marchand. Kelly thought it went well during Game 1, but Julien indicated on Sunday that he's going to take the next two days to figure out if he'll tweak his line combinations.
Even before Kelly came to Boston in a trade-deadline deal with the Ottawa Senators, he knew how important Bergeron was to the Bruins.
"There was no secret before coming here that Bergy is a consummate professional on and off the ice," Kelly said. "There's a reason he's an assistant captain on this team at 25, and has been for a while. He's a leader in this room, on and off the ice, and he plays the game the way it should be played. He's fantastic at both ends and it'll be nice to get him back."
Kelly hasn't been the only Bruins player affected by Bergeron's injury. With a hole to fill, Julien decided to give rookie Tyler Seguin his first taste of the Stanley Cup playoffs. The 19-year-old forward had been a healthy scratch for the first 11 games of the playoffs.
Bergeron wasn't as high profile during his rookie campaign in 2003-04 (when he was 18) as Seguin, the No. 2 overall pick in 2010, was this season. The difference, however, is Bergeron enjoyed great success from the start and has been an important part of the Bruins organization from day one.
Seguin has learned from the veteran, especially seeing how Bergeron had played in the playoffs prior to the concussion.
"Like [Mark Recchi] and some of the other established guys, he's a good guy to look up to," Seguin said. "Seeing how focused and the type of leader Bergy is on and off the ice, he's a good guy to follow in the footsteps of."
When a trip to the Stanley Cup is at stake, players will do whatever they can to play.
Current San Jose Shark and former Bruins captain Joe Thornton is a perfect example. In 2004, Thornton suffered torn cartilage in his rib cage late during the regular season, but the extent of the injury wasn't made public until after the Bruins lost in the first round of the playoffs to the Montreal Canadiens and Thornton went seven games without recording a point.
But concussions and head injuries are completely different, as the Bruins know all too well. Another of their top centers, Marc Savard, was limited to 25 games this season and had to shut it down in February after suffering his second concussion in less than 12 months.
There's no doubt Bergeron wants back in. But this is the third concussion of his career and the organization will proceed with caution. The last thing the Bruins want is a situation similar to that of Savard.
Joe McDonald covers the Bruins for ESPNBoston.com.