The Boston Bruins and general manager Don Sweeney are still working hard to get Brandon Carlo and Charlie McAvoy under contract. 

Out of the two, McAvoy will likely land the bigger contract and that was the original indication on why no deal has been made yet. 

However it might not be McAvoy's contract demands that are stalling the talks. 

It's not that the Bruins might think that McAvoy is overvaluing himself, the Bruins might be hesitant to dish out any big offers because of McAvoy's health card. 

According to Fluto Shinzawa of The Athletic, it could actually be a huge concern. 

“The Bruins’ concern here is health: McAvoy has suffered heart and concussion issues and has yet to play more than 63 games in a season.
“The Bruins will try to dig in a little bit. They’ll point to his games and they’ll use [David] Pastrnak, who’s a superstar. It’ll be a tough deal to do, a tough deal to evaluate. It may end up that a solution is four years,” an anonymous agent told Shinzawa.”

According to Shinzawa, McAvoy has already rejected an eight year deal worth $7.5million a season. 

Source: The Athletic