The Pole has taken maximum points in his Citroen DS3 RRC in four of his six outings to date, and starts his final nominated round with an eight point advantage over Abdulaziz Al-Kuwari.
The Qatari is absent this weekend but even if he wins the final round at Wales Rally GB next month, it will not be enough if Kubica takes first or second in Spain.
The opening two legs are on fast and smooth asphalt roads, the closest the WRC comes to race circuit conditions, and few would bet against the ex-Formula 1 driver sealing the crown here.
However, the 14-strong entry boasts a number of drivers capable of pushing Kubica all the way.
Elfyn Evans finished second behind him in both Germany and France and the Welshman could pose the strongest challenge in one of six Ford Fiesta R5 cars lining up.
Sepp Wiegand, who led the category after the opening round in Monte Carlo, returns for the first time since Rallye Deutschland in a Skoda Fabia S2000. A strong performance could see him leap from fifth to third in the standings, relegating Yuriy Protasov, who has completed his seven nominated rounds, and Nicolas Fuchs.
However, Fuchs is back for the first time since Rally Italia Sardegna. The Peruvian tackled six of the opening seven rounds and his pace in the first half of the season was sufficient to earn him the FIA WRC 2 Production Car Cup title in a Mitsubishi Lancer Evo X.
Also in Fiesta R5 cars are Rashid al Ketbi, Lorenzo Bertelli, Ala’a Rasheed, Subhan Aksa and Robert Barrable. Tunnock’s World Rally Team driver Barrable was a regular in the top three stage times at Rallye de France earlier this month and has developed a feeling for the roads after spectating on the rally for the past two years.
Yazeed Al Rajhi drives the older specification Fiesta RRC but he has shown strong pace during a season shortened by injury. Despite having started only three rallies, the Saudi Arabian is seventh in the championship.