Monaghan will undergo wrist surgery shortly and has also been dealing with a painful hip issue.
"This isn't something that just happened,'' said GM Brad Treliving. "We're talking not just one significant injury, but two. Injuries that in a lot of cases would've keep a guy from playing at all.
"He's been trying to muscle through as best he can and showed a lot of determination doing it. He said: 'I'm good. I can manage it.' And we tried to.
"But it's just time now. We've had to step in and say 'Okay, enough's enough. You've got to get this looked after.' He can't function.
"The hip needs to settle down a bit but he'll have a procedure on the wrist and it'll be a rehab process over the spring.
"That's where we're at."
Operating in obvious discomfort, kept off the ice during practice time, the Flames' leading poacher had connected only twice in the team's most recent dozen games. He was clearly labouring.
"I think any player will tell you that after Day One of training camp they're not feeling great and after that it's just levels, degrees, of stuff to deal with,'' said Treliving.
"I can't remember the last time he practiced. The way the schedule is now, it's so compressed, so relentless, for everybody, that there's no week to say 'Okay, we can do something here.' You're playing every other night.
"That's the reality. But it's a tough reality when somebody's trying to deal with one injury, let alone two."
The injury bug has bit hard the last month.
The Flames also announced Friday that Kris Versteeg, who missed 48 games due to hip surgery, will also be sidelined for the rest of the campaign.
"It's that time of year; that's part of the game, too,'' said coach Glen Gulutzan of a growing list of banged-up bodies.
The Flames move on for a date at the Staples Center against the L.A. Kings after Saturday's afternoon game.
"Obviously it's tough,'' conceded winger Curtis Lazar, "but you've got to credit those guys for trying to fight thorough the injuries. These games, at this time of year, are tough to play, tough to win.
"So for those guys to suck it up and fight hard for our hockey club means a lot.
"We talked about it in our meeting this morning - how you handle yourself, how you carry yourself as a person. You learn a lot about true character when things are going as ideally as you'd like."
For any professional athlete, Monahan's struggles are extremely difficult: Understanding you're not near your best, knowing how important you are to the enterprise as a whole, wanting to give more but faced with the stark reality that it's just not happening.
"Their mind and their will are accustomed to them doing certain things,'' said Treliving, "and when the body doesn't allow them do those things … it's hard."
That reality is familiar to virtually everyone in the dressing room.
"Mony's a quiet guy so people might not see the character and the passion he has,'' said captain Mark Giordano.
"But he wants to win as much as anyone I've seen. He has that drive.
"It's tough sometimes watching someone struggle through an injury but Mony's that's type of guy. He's our best scorer, offensively he's a catalyst for us. Him and Johnny really make things happen.
"He wants to be that difference-maker for us."
