Coleman was helped from the field at halftime on Friday at the Gabba after his left leg clashed with Carlton tackler Lachie Fogarty as he kicked.
The Lions had blitzed the Blues early but in the third term had eight-straight goals kicked on them in a 13.8 (86) 12.13 (85) loss that ended a 14-game winning streak at the Gabba stronghold.
Initial reports were of a hyper-extended knee for Coleman but coach Chris Fagan delivered worse news of a likely season-ending injury in the post-game press conference.
"He'll get a scan tomorrow, but at this stage it looks like an ACL," Lions coach Chris Fagan said in the post-game press conference. — AFL (@AFL) https://t.co/BwVyTjd9eTMarch 8, 2024
"He'll get a scan tomorrow but at this stage it looks like an ACL," he said.
"We haven't had much luck with ACLs, think about (Eric) Hipwood, (Cam) Rayner, Ashy (Will Ashcroft) last year.
"That's not confirmed, but it's more than likely."
Conor McKenna could return from a hamstring injury next week while Ashcroft won't be back until the later half of this season after his setback in 2023.
But Coleman's ball use and dare out of defence will be hard to replace, the 23-year-old dominant in the first half of last season's grand final.
"We get disappointed for all the lads with those sorts of injuries, because we know the way back's a long way back," Fagan said.
"It'll create an opportunity for somebody else, which will be their good fortune."
Fagan rattled off the statistics after the game as if to figure out what went wrong, but admitted he wasn't quite sure.
"We don't walk away from what happened tonight," he said.
"It wasn't a terrible performance, it was just a really bad one quarter.
"We need to chat about it and address it.
"You need to sleep on it, need to watch the vision and get the absolute truth of what happened and understand that."
Veteran defender Darcy Gardiner (11 disposals) started in the opposition's goal square while Cameron Rayner was at the first bounce and veteran Dayne Zorko was best on ground in the first half up front.
"We'll keep trying things, because we have to get better," Fagan said of his positional tweaks.