A literal dark cloud has descended over this weekend's Singapore GP.

Local reports say forest fires in Indonesia have made the air unhealthy to breathe in the city-state.

Promoter Singapore GP issued a statement saying a "plan" is now in place.

"In the event that the haze causes visibility, public health or operational issues, Singapore GP would work closely with the relevant agencies before making any collective decisions regarding the event," it said.

Meanwhile, if the race goes ahead as planned, Ferrari has warned that it is unlikely to complete a hat-trick of victories.

Charles Leclerc won at high-speed Spa and Monza, but team boss Mattia Binotto said: "We will have more trouble again in Singapore."

And he doesn't think the gap to Mercedes will be closed before the end of the season, either.

"I do not think we will catch up our deficit on circuits that require maximum downforce. The gap is too big for that," said the Italian.