BRISBANE Lions captain Dayne Beams will miss up to a month after scans on Monday confirmed he has strained the AC joint in his left shoulder.

Beams suffered the injury in the opening minutes of Saturday's loss to Greater Western Sydney following a heavy hip-and-shoulder from Shane Mumford.

The club confirmed the injury to AFL.com.au, saying Beams would miss three or four weeks.

It is a huge setback for coach Chris Fagan and his team, who are already missing experienced duo Allen Christensen (collarbone) and Mitch Robinson (foot) for the season.

Beams missed two games earlier this year with a quad problem, but thankfully the latest injury is the opposite shoulder to the one he had reconstructed in 2015.

Vice-captain Tom Rockliff stepped up to lead the team in Beams' absence earlier this season and is likely to do so again on Sunday against Essendon.