Krug will wear a protective boot and be re-evaluated in three weeks.
General manager Don Sweeny said Monday that Krug's latest injury is unrelated to his broken left ankle from Game 4 of the Eastern Conference Second Round against the Tampa Bay Lightning on May 4.
"You work really hard, especially throughout the summer, to feel comfortable and put yourself in a position to get back in the lineup," Krug said. "It felt like I was just starting to work through timing issues and getting my gap back and things like that, and all of a sudden I have another setback. It's frustrating. It's unfortunate, very unlucky. Kind of a freak thing."
Krug said he was trying to clear a puck out of the corner when his ankle got caught in a groove in the ice as he was getting hit. He continued playing before heading to the dressing room to be examined by doctors.
"It's re-evaluation in a few weeks," he said. "Hopefully everything feels good by then and I can start to get going on the ice. Now it would be ignorant to think that after three weeks off of the ice that you can jump in and go ahead and play in action, play full-go. It's just very unfortunate and we'll see where it stands after that."
There was some good news for the Bruins on Monday, when forward Patrice Bergeron practiced for the first time since the start of training camp. He had been recovering from offseason groin surgery and dealing with back spasms that started before camp opened.
Bergeron said he has been feeling better every day, and that the practice allowed him to see how his body handled the contact.
"It felt really good," he said. "No issues. Everything went according to plan. Get another good practice in [Tuesday] and be ready for Wednesday."
Though the top-line center did not play in a preseason game, he is expected to be in his usual place between Brad Marchand and David Pastrnak for the regular-season opener against the Washington Capitals at Capital One Arena on Wednesday (7:30 p.m. ET; NBCSN, TVAS).
"Not setbacks at all. Participated in every drill," coach Bruce Cassidy said. "Anticipating he'll be ready to go Wednesday."
While acknowledging that it isn't optimal to have not played in a game since the Stanley Cup Playoffs last season, the Bruins are not worried about Bergeron.
"I would suspect he would have preferred to play a game or two," Cassidy said. "I think that's human nature to [want to] shake the rust off. I think he also understands that when you have an injury you've got to make sure you get yourself ready to go for the regular season. Much more important than an exhibition game or two. He'll get up to speed in a hurry, just the type of player he is."
Bergeron also will be on the first power play if he plays Wednesday, as Krug likely would have. Finding a player to replace Krug will be a challenge for Cassidy and his staff.
"We'll have somebody young up there, more than likely [Matt Grzelcyk] or [Urho] Vaakanainen or Charlie [McAvoy]," Cassidy said. "Those are our offensive [defensemen]. There will be a bit of a learning curve there so we'll have to probably simplify it, get it into [Pastrnak's] hands a little more often, maybe less movement, more pucks to the net, and rely on the other group to pick up some of the slack."
Grzelcyk spent practice Monday in a non-contact jersey but is progressing well in his recovery from a lower-body injury and could be ready to play Wednesday, Cassidy said. Grzelcyk was paired with Steven Kampfer at practice.
