F1 threatened to burst into a new controversy on Saturday as the FIA moves against blown exhaust diffusers.
The governing body intends to clamp down on the off-throttle blowing of exhausts within the next few races.
But Charlie Whiting, the FIA technical delegate, admitted to reporters late on Friday that the technology is in effect already illegal, due to the wording of the regulations about driver-assisted aerodynamic aids.
It means Virgin, HRT and perhaps Williams, the teams not using sophisticated blown exhausts in Spain, could theoretically protest the outcome of the Spanish grand prix -- a risk Whiting acknowledges.
"I've made that clear to the (other) teams," he said. "It (a protest) could happen and then we'll just take it to the stewards in the normal way."
That could result in most of the field being disqualified, an outcome that reminds of the farcical 2005 US grand prix, when only six cars had tyres suitable to race.
"I'd like to think that probably wouldn't happen but one never knows. It's not beyond the realms of possibility," said Whiting.
The possibility moved closer to reality on Saturday morning, when it emerged that the Virgin cars have in Barcelona reverted to its Shanghai-specification exhaust layout overnight.
Currently we have no intention of protesting anything at all
The back-of-the-grid team has been trying to introduce a blown exhaust in Turkey and in Friday practice in Spain, but Saturday's news means the car is now technically one of only two or three legal ones in the entire Barcelona field.
Team president Graeme Lowdon confirmed to the British broadcaster BBC that the decision to revert to the old layout is related to the blown exhaust controversy.
"Currently we have no intention of protesting anything at all," he said, adding that the chance Virgin might change its mind later is "highly unlikely".
"We're just ensuring our car is legal in the event that someone protests against us," added Lowdon.
Ostensibly for technical reasons, Williams was uncommitted late on Friday about pushing ahead with its own blown floor this weekend, while team chairman Adam Parr confirmed that it was the British team that recently asked the FIA about the legality of the systems.
"Yes, we - and I don't know if we are the only team - but we have checked the situation with the FIA to make sure before we spend a lot of money," he said.