"It was a pretty significant amount of pain," Rielly told The Athletic's Jonas Siegel. "But I did my MRIs and everything like that and there was no damage to the real important things. So it was just a matter of pain management."
Rielly added that it wasn't one specific incident that caused the discomfort, but instead "normal wear-and-tear stuff" that built up over time.
"We took some action over the Christmas holidays and I'm feeling much better after some minor stuff that we did," he said. "And I think it's just having confidence - and the pain is way lower than it was, and I’m able to just go out and play more."
Despite the injury, Rielly hasn't missed a game this season and believes he's getting closer to full health.
"I mean, I feel healthy," Rielly said. "And there were times earlier when that wasn't always the case. But I think right now it's just focusing on little things and playing within the structure and making sure you put certain things way before yourself. That's about trying to lean toward that thing where the team just gets rolling.
"That's my only focus right now."
After breaking out with a career-high 72 points and finishing fifth in Norris Trophy voting a season ago, Rielly's production has slowed down drastically in 2019-20. The 25-year-old is currently on pace for 47 points and hasn't scored a goal in the last 20 games.
However, Rielly still leads all Leafs skaters in average ice time at 24:19. He's also seen his underlying metrics improve since being partnered with Tyson Barrie - who's replaced him on the first power-play unit - on the top pairing under new head coach Sheldon Keefe.
The Maple Leafs currently sit third in the Atlantic Division with 53 points, one shy of the Tampa Bay Lightning with two extra games played.