McAvoy conditioning is a concern going down the stretch run, but he will be pushed to maintain his edge by fellow teammate Patrice Bergeron, who is also recovering from an injury.
"Clearly, Bergy [Patrice Bergeron] knows what to expect coming out of it," said Cassidy. "We'll get him to talk to Charlie about what to do between now and then so that you don't drop off. It's natural when you don't play this time of year. Especially when the intensity goes up. You're going to lose a little bit of your edge.
"He has to find a way to keep up with his conditioning and keep mentally sharp during this stretch of time…We will rely on Bergy in that area a little bit to keep him focused as best he can without actually being in the lineup."
Cassidy maintained that the team will try to take any positives they can from the situation, including the opportunity to play more of their defenseman.
"It allows other players to go into different roles and allow the player to have a bit of breather during the stretch run," said Cassidy. "That's the way we're looking at it. Hopefully he comes back healthy and ready to go."
With 19 games remaining, the team will look to have McAvoy back prior to the start of the playoffs.
"Assuming its on that timeline, he'll have a little bit of time to get ready before playoffs," said Cassidy. "Again, that's still a stretch away, I don't know how that will all play out…We'll see when Charlie comes back, how important are the games versus how important is it that he gets back in the lineup? How much time will he need? Those are questions that we will try to get back in front of and he's ready to answer."
While the goal is to have McAvoy back into the lineup before the playoffs, there is comfort in knowing he has experience jumping straight into the intensity of the playoffs.
"I think that does help him," said Cassidy about McAvoy's experience last season of being dropped into a playoff series. "It allows us a little comfort that if he doesn't get a lot of time before and if he is ready come playoff time, he has been through it."
With McAvoy out, Brandon Carlo will replace him on the first pairing alongside Zdeno Chara. The second pairing will see Nick Holden shift over to the right defense position and play next to Torey Krug. Matt Grzelcyk is back to full strength and will rejoin the lineup alongside Kevan Miller.