SOCHI, Russia - Two years ago, Red Bull was unbeatable in Formula One. Now it could pull out of the sport altogether.

The team's relationship with longtime engine supplier Renault has collapsed acrimoniously in what seems set to be Red Bull's first winless season since 2008. Without an engine confirmed for 2016, it is far from clear whether Red Bull and its Austrian drinks baron owner Dietrich Mateschitz will be back.

It's not just fans who are confused about the rapid turnaround. World champion Lewis Hamilton is, too.

"It would be a shame for the fans (if Red Bull pulls out)," the Mercedes driver said Thursday. "It seems really odd for me, having witnessed Red Bull's success and then in the moment that they don't have success, they've been upset about it. I've not seen that with any other team."

He added that when big teams like Ferrari have gone through lean spells in the past, "I didn't hear them complaining the next year."

If Red Bull and its sister team Toro Rosso were to go, the F1 grid would shrink to 18 cars for 2016, even with the arrival of American team Haas.

Among the drivers in jeopardy is Daniil Kvyat, who has settled in well in his first season with Red Bull, finishing second in Hungary in July. He now goes into his home race in Russia with little clarity over his future.

"Formula One is a rough world, you have to be patient. You have to consider that it's not a honeymoon at some points," he said. "I think the right decisions will be taken in the future from our bosses ... I rely on them fully."

The longer Red Bull waits to secure engines for 2016, the harder next season will be. Teams are already hard at work on designing next year's cars, but without a power unit, they can't design a complete vehicle.

"Obviously it starts to be a bit late and we need to design all the rear part of the car," Toro Rosso's Carlos Sainz said. "When you don't have something at the rear at this stage of the year, it's a bit tricky."