A mysterious Mercedes mule has been spied undergoing testing.

Caught wearing a modified E-Class body, the prototype has been equipped with canards and extended fender flares which suggest the model has a wider track than your typical sedan. More notably, the mule has shrunken rear doors which indicate the production model will be extremely short. This likely means Mercedes is testing either a coupe or a convertible.

Nothing is official, but it’s believed the model could be a mule for the next-generation SL. That’s well within the realm of possibilities as Mercedes-AMG CEO Tobias Moers has previously said we can expect to see SL prototypes on the road this year.

The company is staying coy on specifics, but Moers has said the next-generation model will be “far sportier” than its predecessor and the roadster will have more in common with the next-generation GT. This could potentially create some overlap between the SL and the GT Roadster, but Moers suggested the company will try to minimize this by keeping the SL focused on comfort and cruising.

Both more are slated to ride on the new Modular Sports Architecture and it’s possible the mule has been created to test and evaluate the platform. Regardless of the mule’s purpose, both the GT and SL are expected to share a number of components.

Rumored to arrive by 2021, the next-generation SL could ditch its retractable hardtop and offer a 2+2 seating arrangement. These changes could help to make the model more competitive with the BMW 8-Series Convertible and Porsche 911 Cabriolet.

Under the hood, we can expect an assortment of hybrid powertrains. Nothing is set in stone, but reports have suggested there will be a turbocharged 3.0-liter six-cylinder engine with outputs of approximately 365 hp (272 kW / 370 PS) and 430 hp (321 kW / 436 PS). There could also be three different variants with a twin-turbo 4.0-liter V8. If the rumor mill is correct, the range-topping model could have over 600 hp (447 kW / 608 PS). The SL could also be offered with all-wheel drive, but nothing is certain as of yet.

Picture credits: S. Baldauf/SB-Medien for Carscoops