Red Bull have hinted at doubts about their future in Formula 1.

The four-time constructors champions are unhappy with their current engine, supplied by long-time partner Renault.

Red Bull have not managed a podium finish so far this season, with drivers Daniel Ricciardo and Daniil Kvyat picking up 30 points between them to leave them fourth in the race for the constructors championship.

In comments to BBC Sport, Red Bull adviser Helmut Marko suggested that the team would like to do a deal with Audi and hinted that failure to do this could see something more drastic happen.

"If we don't have a competitive engine in the near future, then either Audi is coming or we are out," he said.