The Singapore Grand Prix is already one of the most physically taxing races on the Formula One calendar, and this year drivers will have to put up with the additional strain of poor air quality.
Smoke from forest fires in Indonesia has choked Singapore in the days leading up to the race, with the local government's Pollutant Standards Index (PSI) wavering between ''unhealthy'' and ''very unhealthy.''
''The haze situation is highly changeable, not only from day to day, but from hour to hour,'' race organizers said in a statement this week. ''Therefore, it is currently not possible to reliably predict what the PSI level might be over the race weekend.''
The organizers will be hoping the air will have improved by Friday when the F1 cars first take to the Marina Bay circuit for practice, and FIA race director Charlie Whiting will consult with teams and drivers on whether any delays will be required.
The concerns over air quality add another challenge for drivers, who nominate this race, along with the grand prix in neighboring Malaysia, as the most physically demanding on the calendar.
Extreme heat and humidity combine with the difficulty of drivers trying to keep their body clocks on European time - sleeping all day - so as to be fully alert for night racing. The street circuit is also bumpy and relentless in its sequence of right-angle bends that allow not even a few seconds of mental and physical respite.
Lewis Hamilton, who won this race last year, will be aiming for a third straight victory after Belgium and Italy to stretch his championship lead over Mercedes teammate Nico Rosberg.
Singapore was decisive in last year's championship fight between the pair, with Rosberg's race destroyed by an electronics failure on his steering wheel, giving Hamilton a points advantage the Briton never relinquished.
Ferrari will go into this weekend's race with confidence it can beat the Mercedes pair. Sebastian Vettel won in hot conditions in Malaysia and Hungary this year, with the Ferrari setup seemingly kinder on tires than the Mercedes on high-degradation hot tracks.
Off the track, most interest centers on the future of the Lotus team, with a further court hearing scheduled for Friday in London. That case will determine whether the debt-laden outfit goes into financial administration.
Renault is in talks with Lotus about buying a majority stake, with negotiations hinging on price and whether the new buyer takes on the debts.
Renault withdrew as a team from F1 after the scandal of the inaugural Singapore Grand Prix, when a deliberately engineered crash and track blockage by his teammate allowed Fernando Alonso to exploit the timing of the safety car and win the race against the odds.
Renault then became a highly successful engine supplier to a dominant Red Bull team, but failed to produce a competitive power unit for the V6 hybrid era which began last year, and public criticism by Red Bull stretched the relationship beyond breaking point.
Renault told Red Bull this week that it would not provide engines to the team beyond the end of this season, despite the existence of a contract until the end of 2016.
''We already alerted the Formula 1 authorities. Don't count on us as a provider of an engine. It's over,'' Renault chairman and chief executive Carlos Ghosn said at the Frankfurt Motor Show. ''You are in the game that when you perform very well you are never mentioned, and when there is a problem with the team you are the first guy to be pointed at.''
That left Renault's future in the sport being either a return as a team in its own right, taking over the Lotus operation, or a very abrupt departure from F1.
''We will either exit or run our own team,'' Ghosn said. ''We don't have a clear decision yet.''
Which option prevails will be influenced by ongoing negotiations between Renault and F1 commercial boss Bernie Ecclestone on whether the French company gets a requested bonus payment for its historical contribution to the sport, in the same manner as Mercedes.
Such a bonus payment could allow Renault to meet the asking price of the current Lotus owners for a buyout.