Dale Earnhardt Jr believes that conflicting engine manufacturers would be the biggest barrier to his proposed ride swap with IndyCar driver Graham Rahal.
Rahal reached out to Earnhardt about the possibility of the pair testing each other's cars via Twitter last week, and was surprised to receive an immediate and favourable response from the NASCAR star.
But while the pair share a common sponsor in the National Guard, Earnhardt said that his affiliation with Chevrolet and Rahal's alignment with Honda would pose a problem.
"I'd have to drive a Chevy," he said on Tuesday.
Rahal admitted that he had not expected Earnhardt to respond so quickly, and remains convinced that the PR potential of such a stunt would be enormous.
"I was surprised he responded," he said. "Of course, I felt with the National Guard that it could potentially happen. But I also thought it would be something that would be fun to do.
"There's been a lot of Cup guys jumping in an IndyCar. Kurt Busch is going to be doing it in the month of May. Jimmie Johnson and others have been interested.
"Getting Earnhardt and a Rahal ... I think the last time those two names were on the same track were the IROC days with my dad [Bobby].
"It would be good to go back out there and see what we could do, have some fun."