Lions physical performance manager Brett Burton told lions.com.au Adcock had carried the injury for a while.
"We were hoping when splinted it would reunite, but it's actually getting further displaced so he'll have the screw put in his finger on Wednesday and we'll know more then about time frames," Burton said.
Adcock's injury comes less than a week after news reliable full-back Daniel Merrett would miss up to 10 weeks with back stress fractures.
It puts a huge hole in the Lions defence ahead of Saturday's home match against Richmond.
Adcock, 25, is having an excellent season across half-back, averaging more than 21 disposals per match, but his injury continues a season full of bad luck for coach Michael Voss.
Captain Jonathan Brown missed eight weeks after sustaining multiple facial fractures in round one against Fremantle, while vice-captain Josh Drummond has played just two matches in 2011 as he battles knee and quad injuries.
The young brigade have also been in the firing line, with 2011 debutants Claye Beams (foot) and Ryan Lester (foot) both out for the season, while Jared Polec (knee) has also missed a large chunk of matches.
