Williams has removed the controversial layout of its 'Coanda'-effect exhaust from its newly-launched 2013 car.
Despite designer Mike Coughlan believing his layout cleverly exploited a loophole in the rules, the FIA reportedly told the British team its solution was not legal.
"Charlie Whiting was here yesterday," British broadcaster Sky's pit reporter Ted Kravitz said on Friday as the Barcelona test concluded.
"(I think) he went to Williams and had a quiet word in their ear that they might want to take that (exhaust solution) off.
"We don't expect to see it reappear given the FIA's stance on that," he added.
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