Rankin joined Crawley in the summer after a spell at Stevenage
Crawley Town have been deducted four points by the Football Conference for fielding an unregistered player - striker Isaiah Rankin.
The move will see the Red Devils drop out of the Blue Square Premier play-off places into sixth place, with 42 points from 26 games.
Crawley were also fined �500, ordered to pay �250 costs, and handed a separate suspended fine of �1,500.
The club will now take legal advice and have 14 days to lodge an appeal.
The punishment follows Rankin's signing this summer, as he was not registered with the Conference at the start of the season even though his contract had been received by the Football Association.
It is the fourth season in a row the club have suffered a points deduction - having been punished for breaching the Conference's financial regulations in 2005/06 and 2007/08, while they started the 2006/07 season with a 10-point deduction after entering administration.
The Conference had earlier imposed a five-point deduction on fellow Blue Square Premier side Oxford United, also for fielding an unregistered player.
A statement on the club's website revealed that Crawley were "extremely disappointed with this decision".
It read: "The decision is even more surprising given the sanction awarded to Oxford United for an identical but much deeper breach of the Football Conference rules."
Meanwhile, chairman Vic Marley added: "This decision is extremely hard to take given the flawed registration procedures that the Football Conference had in place in the early part of the season.
"I have sympathy for Oxford, who like ourselves are a victim of this flawed process, but there is no doubt we have been dealt far more severely."
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