Rankine is the sixth AFL-listed player banned for a homophobic slur against an opponent in the past 16 months.
The AFL initially delivered a five-game suspension, which was reduced when the Crows made a "compelling medical submission", AFL chief Andrew Dillon said.
Dillon and Adelaide CEO Tim Silvers refused to detail the nature of the medical submission.
But Silvers admitted he was "nervous" for Rankine's mental health.
"He put himself into this position and he's deeply remorseful and regrets what he said," Silvers told reporters in Adelaide.
"But he's doing it pretty tough. He basically hasn't left his house for the last few days."
Rankine will only play again this season if ladder-leading Adelaide lose a qualifying final but then advance to the grand final, when the 25-year-old would be available for selection.
Adelaide play North Melbourne on Saturday in the last home-and-away round and will then host two finals.
AFL boss Dillon defended the reduction of the league's initial proposed ban.
"It was a compelling medical submission but I will not go into the detail," Dillon told reporters in Melbourne.
Describing the suspension as "significant", Dillon denied it was designed to give Rankine hope of playing in the grand final.
"A game is a game," he said.
But Crows chief Silvers said the fact Rankine had a glimmer of grand final hope was important.
"It's nice that there's a carrot for him and that it means his season, potentially, is not over ... that is good for his mental health," Silvers said.
Rankine directed a homophobic slur to an unnamed Collingwood opponent in Adelaide's three-point win last Saturday night.
"I regret using the word and I am deeply sorry for doing so," Rankine said in a club-issued statement.
"That type of language has no place in football or in the community.
"It was a mistake and I have apologised to the Collingwood player. And what happened does not reflect my values or those of the club.
"I'm committed to educating myself and being better."
Silvers said his club was "frustrated and disappointed" in Rankine, who will now likely spend time away from the city of Adelaide.
"He might need some time out ... we're looking at some options to potentially just get him away and get him out of the Adelaide environment for a week or so," he said.
Silvers was upset the AFL integrity unit's investigation, launched last Sunday, was leaked to media.
"I'm disappointed that we had to deal with leaks throughout this process because it's supposed to be confidential," he said.
"There was some information that was right and some misinformation as well."
Silvers said his club didn't use claims of AFL hypocrisy for hiring Snoop Dogg for grand final entertainment as part of its submission.
The rapper has released songs using the same homophobic slur - f****t - that Rankine directed at the Collingwood player.
"That wasn't part of our submission," Silvers said.
"We're striving to be in the grand final, there's no doubt about it. I don't think we're too focused on the grand final entertainment."
Last month, West Coast's Jack Graham was banned four games for a homophobic remark to a GWS player.
In April last year, Port Adelaide's Jeremy Finlayson was suspended for three games and, the following month, Gold Coast's Wil Powell was suspended five matches, both for directing homophobic slurs at opponents.
Two VFL players - Sydney's Riak Andrew (five games) and St Kilda's Lance Collard (six matches) have also been banned for on-field homophobic comments.
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