Krug re-injured the ankle during the Bruins' preseason finale on Saturday night and will be in a boot for the next three weeks. After that, he'll be re-evaluated to determine the next step in his recovery.
"You work really hard throughout the summer to feel comfortable and put your self in position to get back in the lineup," said Krug, who confirmed that the injury was unrelated to his previous fracture. "Obviously 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'm going to have another setback.
"It's frustrating, it's unfortunate, very unlucky, and kind of a freak thing. But it's part of it and you've just gotta work through it and have the right attitude and continue to work."
Video: Krug talks latest injury
The 27-year-old was playing in his second preseason contest since being cleared for game action when he caught a rut as he was taking a hit in the corner during the first period. Krug attempted to play following the injury, but after a few minutes retreated to the dressing room.
"I wasn't in too much pain right away, probably the adrenaline of the game and things like that," said Krug. "But as the period went on, just wasn't able to finish and got closer to the end and decided to go to the room and get some attention from the medical staff. They obviously did their job and started to realize something was wrong."
This is the second consecutive season that Krug was injured in the preseason. Last fall, the defenseman suffered a broken jaw during the second preseason game, causing him to miss the opener.
This time around, patience will once again be required.
"Hopefully everything feels good by then and I can start to get going on the ice," said Krug. "It would be ignorant to think after three weeks off the ice that you could jump in and go ahead and play and jump in full-go.
"So there's probably going to be a period of time where you ramp things up. It's just very unfortunate. We'll see where it stands after that."
In the interim, coach Bruce Cassidy must decide how to fill the hole. It appears that Matt Grzelcyk has the early edge, but a lower-body injury has put his availability for Wednesday night in question. Should he not be ready, Cassidy could turn to rookie Urho Vaakanainen or veteran Steven Kampfer.
"Right now, Vaakanainen - three lefts, three rights is kind of the way we're looking," said Cassidy. "But we'll make that decision once we hear about Grizz. Vaakanainen's been very good, so has Kampfer. So whatever direction we go we feel comfortable."
Grzelcyk skated in a red non-contact jersey during Monday's practice and is optimistic about his chance of playing against the Capitals on Wednesday night.
"I felt good, progressing well and hopefully can join the team [on Tuesday] full-go," said Grzelcyk. "Excited about that and hopefully excited to get in on Wednesday. I feel like I am [on schedule]. It's obviously up to the coaches to make the decision roster-wise, but I feel like I should be able to go by then."
Should he get the call, Grzelcyk is likely to see some power-play time with Krug sidelined.
"I think power play is something I grew up playing, would like to kind of showcase that if I get the opportunity," he said. "But obviously hopefully we can get Torey back as quick as possible because he's one of the best defensemen in the league.
"It's definitely going to hurt having him out. Hopefully we can try to do our best while he's gone."
Video: Krug out, Bergy returns
Bergeron Feeling Good
In some positive injury news, Patrice Bergeron ditched his non-contact jersey for a normal white practice sweater on Monday and appears ready to go for Opening Night.
"Feeling better every day and it was good to get another practice in and a pretty good skate, actually," said Bergeron. "Still shooting for Wednesday, there's no changes. Status quo, I guess. Looking forward to it."
Video: Bergeron talks being ready for WSH
Still A Chance
Neither Daniel Winnik nor Lee Stempniak, both in camp on professional tryout agreements, practiced on Monday, with Sweeney saying both players may have other opportunities.
"Daniel Winnik has another opportunity he's currently exploring, so we're going to be in contact with him over the next few days to see what ultimately is his decision and ours, so we both explore things," said Bruins general manager Don Sweeney. "The same thing with Lee. Those PTOs will expire officially on [Oct. 3] as rosters open up. It doesn't mean Lee won't stay with us and continue to play with us."
Down to the Wire
Sweeney announced more cuts on Monday, assigning forwards Trent Frederic and Peter Cehlarik to Providence.
"He had a very good camp," Sweeney said of Cehlarik. "Was productive, made a lot of high-end plays in the offensive zone, which he's very capable of doing. We covet the size that he has, the ability to play both sides of the ice. Some details when he doesn't have the puck need to continue to be cleaned up.
"He missed a lot of time last year with injury, but he's knocking on the door."
With Frederic being sent down, that leaves Sean Kuraly as the likely winner of the Bruins' third-line center competition and Noel Acciari manning the middle of Boston's fourth line between Joakim Nordstrom and Chris Wagner.
"The other night looked like it's exhibition, the first time they've been together as a line," said Cassidy. "They look like they can handle it, and part of being productive in that role is protecting the puck in the other end of the ice, forcing the better offensive players to go 200 feet and defend first. And they did a real good job with that, so that would be a real positive for our team and a real good thing for Bergy's health and stamina through the course of an eight-month season."
Video: Bruins brass holds press conference
Monday's Practice Lineup
Brad Marchand - Patrice Bergeron - David Pastrnak
Jake DeBrusk - David Krejci - Danton Heinen
Ryan Donato - Sean Kuraly -David Backes
Joakim Nordstrom/Anders Bjork - Noel Acciari - Chris Wagner
Zdeno Chara - Charlie McAvoy
John Moore - Brandon Carlo
Urho Vaakanainen - Kevan Miller
Matt Grzelcyk - Steven Kampfer