Kamui Kobayashi has effectively called time on his pursuit of an F1 seat for 2013 after Romain Grosjean was confirmed as returning to the Lotus line-up.

Sauber refugee Kobayashi - ousted by the Swiss team's decision to hire Nico Hulkenberg and Esteban Gutierrez for next season - had been hoping to step into the seat alongside Kimi Raikkonen for 2013, but Grosjean's confirmation, hot on the heels of his Race of Champions success on Sunday, all but closed the door on the Japanese favourite.

With only Force India, Caterham and Marussia having vacancies - and each having more likely candidates than Kobayashi lined up to fill them - the Suzuka podium finisher published the following open letter on his personal website, explaining his situation to the fans that helped launch a fund to secure a seat in the top flight for 2013.

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"To all the fans,

"Thank you for the big support. I am very appreciated that many of you have donated and trying to make donation. I must mention this that since the donation started, it has become quite big news in Japan. And because of your big support, it gave huge influences to some of Japanese companies and I started receiving good support from them.

"And I was in the position to bring a budget of 8 million Euro at least. If you could imagine the time I had, it was overwhelming reaction and it shows there still is a great potential from Japanese companies.

"Unfortunately, the time was still short and I am not able to secure the seat with competitive F1 team for 2013. I have to admit that it is very sad and feel sorry for fans and Japanese companies who supported me. But I am still confident to make it happen in 2014.

"I would like to stop the donation for now and while I will save all the money for 2014, I start to look what is the best option for 2013 and also 2014. My main priority is to secure the competitive F1 seat in 2014.

"I have no interests to race any other categories.

"I will make an announcement as soon as I make a decision for 2013. So, please wait and really looking forward your support for coming year, too."

Kobayashi's F1 career includes 60 starts, mostly with Sauber but also three races with Toyota that kick-started his spell in the top flight. He amassed 125 points in that time, 60 of which came in 2012, including that emotional podium in front of his home fans at the Japanese Grand Prix.