The injury was unusual, which made the prognosis more uncertain and threw his World Cup plans with the All Blacks into disarray. It said much about his mental strength and recuperative powers that he returned to rugby just in time to give a sparkling performance in the tournament.
Dagg's assist for Ma'a Nonu's try in the semifinal win over against Australia, when he made a break and flung a pin-point one-handed pass, was one of the more memorable highlights of the World Cup.
Now he is beginning the new season slowly and easing his right quadricep into action. But his thoughts aren't far away from last season when he spent much of his time with his feet up and waiting for the next shake.
"It's good to get out of the house and be at [Crusaders training centre] Rugby Park for the day," he says. "When you're running around on the field you can't really feel those little [shakes]. It's only when you're in our two-storey apartment that you feel them. Those ones that happen at 2.30 in the morning aren't so good, though.
"I wasn't used to it, especially when it first happened. I hadn't witnessed something like that, I don't think anyone has - coming down and your house is always shaking and everything's destroyed and there's not much happening, especially when you've got an injury and there's not much going on for you."
Having expended so much emotional and physical energy into getting fit for the World Cup, and then displacing Mils Muliaina as the country's best fullback on the way to winning the Webb Ellis Trophy for the first time in 24 years, it's perhaps not surprising Dagg feels flat on his return to Super Rugby.
"It's been quite hard getting that little bit of motivation, but it's my job and I love playing rugby," he says. "It doesn't take that long for me to get motivated. It's just that first step of getting down here, and getting to training for that first day was probably the hardest.
"It [the World Cup] is such a long tournament and it takes a bit out of you, so when you get your break, you just want to enjoy it and you get to that point where you don't really want to go back. But it's like anyone returning from holiday, you have to do it.
"Coming down from such a high ... but that's all behind me now. It's a new year with the Crusaders and we want to go that one step further and win this title."
Consistency is key for the 23-year-old, who had a brush with controversy at the World Cup when he was seen out drinking during the week of the quarter-final against Argentina. Luckily for Dagg, who was injured with a haematoma at the time, and drinking partner Cory Jane - who turned in an outstanding performance against the Pumas before delivering his apologies to the media and public - the incident was forgotten amid the All Blacks' triumph.
Crusaders backs coach Daryl Gibson says Dagg has got all the physical attributes to be an outstanding fullback for many years if he can improve that one aspect of his game.
"Everyone saw at the World Cup what a fantastic comeback from injury he made," Gibson says. "We saw some real genius in his play and that's something we want him to replicate on a consistent basis. If he could do that, he could be the No 1 fullback in the country for the next 10 years - like Mils was. There's still some way to go but he's a tremendous asset to the Crusaders and New Zealand rugby."
