PARIS (AP) — Having threatened to skip the last two races of the Formula One season because of a pay dispute, former world champion Kimi Raikkonen will now miss them anyway because of back surgery. Lotus said in a statement Sunday he is out for next week's United States Grand Prix and the season-ending Brazilian GP at the end of this month. His replacement will be announced in "due course." The 34-year-old Raikkonen has had back pain in recent months and almost missed the Singapore GP in September when the problem flared again. His Lotus career, in effect, is over because he will drive for Ferrari next year. One possibility for Lotus is to promote third driver Davide Valsecchi, although the 26-year-old Italian has no F1 experience, or to hand reserve driver Jerome d'Ambrosio the seat. The 27-year-old Belgian has 20 Grand Prix starts and was drafted into Romain Grosjean's car for last year's Italian GP after the Frenchman was banned for a race. At last weekend's Abu Dhabi GP, Raikkonen criticized the team for not paying his salary this season and threatened to pull out of the final two races of the season in protest. He had to be persuaded to race in Abu Dhabi but skipped his media obligations on the Thursday before the race. He pulled out of the race on the first lap because of suspension damage after a minor collision. He then got in a van and drove away, refusing to answer any post-race questions. The weekend before, tensions surfaced within the team. Raikkonen was upset when he was ordered by the team's trackside operations director, Alan Permane, not to hold up Grosjean during the Indian GP.