The Buick Avenir concept car is unveiled at the North American International Auto Show in Detroit. The large rear-drive vehicle could be a flagship sedan in Buick's lineup.

DETROIT — It looks like General Motors’ Buick will soon get a big, sporty rear-drive sedan. On the eve of the first press day at the Detroit Auto Show, the company unveiled the Buick Avenir, a coupe-like four door with an athletic stance.

For now it’s a concept car and GM won’t say when or if it will be built. But Buick lacks a large flagship sedan that would compete with highly profitable German and Japanese luxury brands.

Product development chief Mark Reuss said Sunday night that Buick definitely needs a car in the segment, but he stopped short of saying that the one GM showed off is it.

The concept car has a 3.6-Liter V6 engine and a six-speed automatic transmission. But those likely are just placeholders. GM said the car was developed jointly in the U.S. and Australia, where many of GM’s V-8 powered rear-drive cars have been designed. It’s likely to have a nine or 10-speed transmission to get better gas mileage.

No price information was available. However, it will cost more than Buick’s current big car, the front-drive Lacrosse, which starts about $33,600.