Gardiner was one of three Lions suspended for striking in the season-opening defeat to the Western Bulldogs, and will miss the clash with Sydney at the SCG on Saturday night.
Fellow defender Harris Andrews is set to fight his three-match ban later on Tuesday night, while Zac Bailey has accepted a one-match sanction.
Bailey and star midfielder Hugh McCluggage (calf injury) will miss the Swans clash, with boom recruit Charlie Curnow set to test the Lions' defensive stocks.
Gardiner, through legal representative Adrian Anderson, argued he was not guilty of striking because his high contact with Bulldogs forward Aaron Naughton last Saturday night did not constitute a strike.
Anderson said it was a double-handed push that resulted in glancing contact with the back of Gardiner's tricep to Naughton's neck.
The Lions also submitted the incident constituted a 'low impact' grading at most, noting Naughton's medical report showed a clean bill of health.
The incident was initially assessed by the match review officer (MRO) as high contact, medium impact and careless conduct.
The Lions compared the incident to one from last season, when Dangerfield's high contact with St Kilda's Ryan Byrnes was deemed low impact and the Geelong champion was fined for striking, rather than being suspended.
But the tribunal rejected Brisbane's arguments, finding the impact was more than negligible and Gardiner's action was a strike.
"We do not accept that it was in the end a push, although it may have started out as a pushing motion," the jury said in its verdict.
"Gardiner's right arm, in particular, extended up and we find that forceful contact was made by the forearm, elbow and tricep region with Naughton's neck and head.
"The impact was more than negligible. The frame-by-frame viewing shows forceful contact was made."
Andrews faces a three-match ban over his contact with the Bulldogs' Arthur Jones, who was knocked out in the incident.
The pair had flown for an aerial contest and when the ball hit the ground, the Lions' skipper threw back his left arm to block Jones' run but struck him in the face.
Jones was immediately treated and taken off with concussion.
The incident was graded careless conduct, high contact and severe impact, drawing a three-match suspension.
Bailey was banned over on a high elbow to Bulldogs debutant Michael Sellwood after the Lions star was tackled over the boundary line.
