Monahan was initially expected to be ready when camp opened.
Defenseman Ladislav Smid isn't expected to play this season because of a neck injury. He had surgery on his neck in 2010 and again in February 2015.
"Everyone knows [Ladislav] has been through a lot with his neck," Treliving said. "We talked pretty regularly over the course of the summer. After seeing our doctors here, [he] will not be playing this year. He's had a long history with it. Right now, physically, he's not able to go.
"We're going to look at [Ladislav] doing some projects for us, in terms of in the front office and maybe having some scouting assignments for him and integrating him in there. But he won't be participating on the ice."
Smid has played a total of 53 games for the Flames during the past two seasons.
"I'm only 30 years old, so I would like to be out there helping the team, but it is what it is," Smid said. "You have only one health. It's not like I'm retiring. But for this year, I'm going to have to sit out. It's obviously hard, but it's not a decision we made overnight. We talked the whole summer. It wasn't just my decision. It was doctors. I heard so many different opinions. We made the decision together.
"My family comes first. I want to be healthy for them and I want to have a normal life after my career. At this point it would be too big of a risk, I feel like, to try to play through my neck issues. I think the year will help me. Hopefully my neck will settle down a little more. Maybe I'll come back and try to play hockey. Maybe not. Maybe I'll try to do something else."