Richard Tuthill's Porsche 911 RGT has been withdrawn from Rally GB after the FIA refused to sign off on modifications needed to run the car in gravel trim.
Tuthill gave his 911 its World Rally Championship debut in Germany in August before handing it over to Francois Delecour for the Rally of France last month.
While the car is homologated to run on asphalt, the different suspension required for gravel stages is not homologated.
Tuthill flew to Geneva late last week in the hope of convincing the FIA's technical department, but they stood firm.
FIA rally director Jarmo Mahonen is sympathetic towards Tuthill's plight and wants to make sure a framework is in place for the 911 RGT to run on the dirt next season.
"It's a pity this hasn't happened," he said. "Richard came to see us last week and we are very grateful for his help on trying to make this happen.
"There are some issues with the technical regulations and some of the suspension parts which weren't homologated. We have seen how spectacular these cars can be on asphalt and we definitely want to see them on gravel as well.
"Our technical department is working to make this happen next year, but part of the problem is that things don't always happen so quickly with this house [the FIA]."
Still hopeful of competing in Wales, Tuthill tested the car in gravel trim last week and ran without any issue.
"We completed the same distance we would do in a day on Rally GB without putting a spanner on the car," he said. "We didn't have any problems at all and the car was beautiful to drive. It felt like it had been born to be driven on gravel.
"It goes without saying that I am bitterly disappointed not to be competing in Wales this week; it would have been wonderful to drive a Porsche on those roads.
"I understand the FIA's decision and thank Jarmo and Michele [Mouton, WRC manager] for their open-minded approach and help all the way along. That said, I can't hide my frustration at the time-consuming nature of a process we began in May."