Hispania Racing (HRT) - the team to have run the greatest number of different drivers over the course of the F1 2010 World Championship campaign - has made its latest change of the season on the eve of this weekend's Singapore Grand Prix, by announcing that Christian Klien is to step in to replace an unwell Sakon Yamamoto.

The revolving driver door at struggling newcomer HRT has been one of the talking-points of F1 2010 to-date, with former iSport International GP2 Series team-mates Bruno Senna and Karun Chandhok beginning the season for the Spanish outfit, before the Brazilian found himself replaced by Yamamoto - again, right at the eleventh hour and in unexplained circumstances - for the British Grand Prix at Silverstone, only to return for the following German Grand Prix at Hockenheim a fortnight later, easing the Indian out of a race seat as Yamamoto stayed put.

With the Japanese ace understood to be able to lay his hands on considerably more sponsorship cash than the man from Chennai - who has since found gainful alternative employment as a popular addition to the BBC Radio Five Live F1 punditry box - it was assumed that he would remain in the cockpit for the balance of the campaign. Not so, it seems.

"It looks as if Sakon Yamamoto has food poisoning," revealed team principal Dr. Colin Kolles, who only a matter of weeks ago brusquely dismissed suggestions that there would be further driver changes ahead. "He doesn't feel well. Because of this, Christian Klien will be driving the car this Friday and for the rest of the Singapore Grand Prix [weekend]. I hope Sakon gets well soon, and is able to drive at his home grand prix in Japan."

The hapless Yamamoto's re-appearance, however, must surely be in some doubt, with many likely to give little credence to the 'food poisoning' line - just like Timo Glock's alleged back and leg injury at Suzuka last year was largely rubbished, enabling as it did home hero Kamui Kobayashi to conveniently step into the breach.

One school of thought is that it has belatedly dawned on Kolles that Hispania would likely be better-served financially by putting all of its efforts into trying to snare tenth spot in the constructors' rankings come season's end - and the greater share of prize money that accordingly accompanies it compared to the eleventh position it occupies at present - than by continuing to benefit from Yamamoto's generous backers.

In order to achieve that goal, the team needs at least one twelfth-place finish or higher over the last five grands prix - and it is assuredly former Red Bull star and BMW-Sauber test driver Klien that offers them the best chance of doing that. The 27-year-old Austrian has already participated in the Friday morning practice sessions in Barcelona and Valencia earlier this year.