But the injury that kept Kelly out for those two midseason months - a broken fibula in his right lower leg - didn't take a toll on him as much as the injury that forced him to miss the entire 2014 postseason.
The alternate captain was sidelined by a herniated disk in his back at the end of the regular season, and never had the chance to suit up for the playoffs. He had back surgery to repair it in May.
"It was probably one of the worst pains I’ve ever had," Kelly said Wednesday following the Bruins' informal practice at Ristuccia Arena. The captain-led practices are taking place before training camp begins on September 18.
"I’ve broken a lot of bones, separated shoulders, but this just kind of crippled me."
Kelly tried to work towards a return during the posteason, but he realized he was fooling himself. The atrophy in his leg caused by the herniated disk was too great; he couldn't get back to playing.
It was night and day for the forward post-surgery. He felt great afterwards. But there was one caveat before getting back into his training routine in his offseason home of Ottawa: six weeks of doing absolutely nothing.
"Normally, with surgery, they want you to start working out right away or start doing something, but with this particular injury they said you’re going to feel better right away and if you try to do something, you could re-aggravate it or re-hurt it," said Kelly.
"So for six weeks, I didn’t do anything. That was difficult. I think that was probably the hardest part of the summer - going home and not being able to do anything, to just kind of sit around."
That doctor's order also meant he couldn't even pick up his two children for six weeks.
"They said don’t do anything, don’t pick the kids up - that was hard. They don’t understand," he said.
For a veteran with nine NHL seasons in his repertoire, being told to not work out or be active is difficult to comprehend.
"Yeah, so I was kind of a skinny fat guy," Kelly smiled to media, with his usual banter. "Skinny legs, skinny arms - not that I have big legs or big arms to start with - but I had a little bigger belly. So I was happy to get started [with training]."
He returned to his workouts in July, and was able to get back on the ice soon after that.
"About the beginning of August, I started feeling much better," he said. "I was getting into a routine, putting weight back on and getting on the ice was a big step."
Throughout his NHL career, Kelly had never encountered an offseason like this past summer, being forced to recover before jumping into a workout regimen. In 2012-13, he sustained the first long-term injury of his career, but was back in action for the end of the regular season and the team's march to the Stanley Cup Final.
"I skated more this summer than I have in I can’t remember how long, which is good. I only played, you know, 55 games, and I was excited to get back on the ice," Kelly said of his long layoff.
The forward finished the 2013-14 season with nine goals and nine assists for 18 points through 57 games.
"So, coming down here is obviously good to be with the guys, and see how they’re doing," he continued.
Now, following more than three months of recovery, Kelly is focused on a strong training camp and a healthy, optimistic start to 2014-15. He doesn't expect to have any limitations when camp opens.
"You know, I think I’m doing everything everyone else is doing," said Kelly. "I’m just making sure I take care of myself a little bit more, stretching before, stretching after. Just making sure I take the time to do those things."
Kelly's also fine to take contact and partake in battle drills. He'd rather not be the target of one teammate's hits, though.
"Oh, not if Zee wants a hit. But everyone else can hit me," he smiled.
With Kelly healed and ready, he's looking forward to a competitive training camp that will see several young players vying for spots.
After the departures of Jarome Iginla and Shawn Thornton, Loui Eriksson will get a shot at the right wing spot alongside David Krejci, leaving openings in the bottom six. Kelly doesn't know what role he'll be called upon to take, whether he'll be at center, or playing on the wing again with Carl Soderberg in the middle. He also doesn't know GM Peter Chiarelli's plan right now or what line Head Coach Claude Julien will have him playing on.
"Every year is the same. You come in, and be a player. Don’t try to be anything else than that," said Kelly. "There’s always speculation, there’s been speculation I think my entire career of you know, where you’re going to play, who you’re going to play with, are you going to be here or are you not going to be here."
"You go crazy worrying about those things. There are more important things to worry about."
And with his injuries in the past, all Kelly's focused on is being in his best shape possible for camp, earning his spot in the Spoked-B, staying healthy and helping the team any way he can.
"That’s what hockey is all about - competing for jobs. Everyone wouldn’t be here or where they’re at in their career if they didn’t compete at some point," he said.
"That’s the luxury of being on this team. Everyone competes for their job and earns their spot every year."