According to Turun Sanomat and Autosport Magazine Kimi is not driving in the final two races because of back surgery next week. It was Räikkönen's manager Steve Robertson who told them the news.
His back has been in bad condition after the practice sessions in Singapore. The car had jumped over a curve and hit the ground just hard enough to make his back ache. It is an old injury from the beginning of his career in Formula One so it did not start this year.
Räikkönen was supposed to have surgery after the season but it could effect his start of 2014 with Ferrari and he wants to be in good shape.
After the surgery he can't drive for 4 weeks so that is why he can't drive anymore this season. This also means that next time he jumps in a Formula One car it is not a Lotus, it's a Ferrari.
Davide Valsecchi will take Kimi's place in the final two races. He was also in Abu Dhabi as reserve driver when Kimi announced that he will not drive anymore. Lotus finally talked him over to race one more time.
There has also been rumors that Nico Hülkenberg would drive instead of Valsecchi. Hülkenberg hasn't got his paycheck from Sauber and is making a protest by jumping to Lotus. The irony is that they haven't payed Räikkönen either at Lotus.