Audi's four-door TT concept leaks ahead of Paris debut

Sketches of a fastback version of Audi's diminutive coupe have appeared on the internet.

If the images are legitimate, and German publication Auto Zeitung claims they are, the car will be nearly 30cm longer than the standard TT to make room for rear-seat passengers and two rear doors.

This would position it as a direct competitor to other 'fastback' vehicles such as the Mercedes CLA, the Volkswagen Passat CC and potentially Audi's own five-door A3 model.

However, it will have four-wheel drive and a tuned 2-liter turbocharged engine that will be capable of putting out 400hp so clearly it has Mercedes and BMW, rather than parent company VW in its sights.

There is a growing trend for manufacturers to take a star model and extend it into its own breakout range.

When BMW revived the Mini back in 2001 it did so with a single car with three levels of performance, but now it is a full-blown range offering coupés, estates and even a soft-roader.

Fiat is currently doing the same with the 500. It's already available as a mini-MPV and an SUV version will be making its debut at the Paris Motor Show next week.

And there's little doubt that the TT has the appeal and the cachet to go beyond being simply a hardtop coupé and soft-top roadster and Audi has already tested the water on numerous occasions over the past 12 months, revealing a two-door shooting break and a crossover SUV take on the car at autoshows.

The fastback would be the third design study of 2014, and while it's merely a concept, Audi more than any other manufacturer has a habit of taking concepts and making them production realities.

Therefore expect to see something very like the TT fastback on a road near you by 2017.