Design complications for Audi's R4 have meant that the future of the mid-engined sports car is uncertain, it has been reported.

According to Autocar, the decision on whether to opt for a steel or alloy body composition has caused a stalling in the creation of the new model.

The news could interest Audi car hire clients keen to see which direction the company will take.

Engineers involved in the production of the model told the news provider that it was unclear whether cheaper but heavier steel would be used over the more expensive but lightweight aluminium option.

"The reaction to the e-tron concept has been overwhelming," a source told Autocar.

"We're weighing up all of the options and possibilities. There's no real-time pressure because we're not replacing an existing model but establishing a new one."

The Audi R4 is expected to be released on to the market in 2012 and be available with both an electric and conventionally-powered version.

Click here to see our range of cars.

Posted by Jenny Denham