Dempsey has been banned for failing to meet the club's "standards and expectations".
A key cog in the team's defence, he will train and play for Essendon's VFL side once he recovers from a hamstring injury (he strained it in a VFL practice match on the weekend).
Bombers coach Mark Thompson said the action was necessary to make Dempsey understand what was expected of him.
“Courtenay is a talented player and an important member of our team. We’ll give him the necessary support required to regain the consistent standards we expect of him as a player at this football club,” Thompson said in a club statement.
“We felt that Courtenay needed to understand that we can’t accept individuals stepping outside of team protocols and requirements.
“We sat down with Courtenay and discussed the reasons why his training standards had dropped, and as a result we agreed the best way forward for him was to go back and train with the VFL side.”
In May 2013, Dempsey was left out of Essendon's round eight team after going on a night out while recovering from an ankle injury.
On that occasion, Bombers football manager Steven Alessio said: "The players set high standards for each other and it's important they don't breach team rules under any circumstances."
Dempsey has battled injury troubles across the pre-season, stemming from a torn hamstring tendon suffered in round 19 last year against Collingwood, which kept him off the park for the rest of the season.
In February, Thompson said on radio that Dempsey "had a bit of a troubled pre-season, so he's in a fitness running program".
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