Mara Yamauchi fears conditions in Osaka at this summer's World Athletics Championships will be even tougher than during Sunday's London Marathon.
Yamauchi managed a creditable sixth place in the women's race
Japan-based Yamauchi was the first British finisher as high temperatures left many elite runners struggling.
She said marathon runners in Osaka will be battling 35C heat and humidity levels approaching 100% in late August.
"Osaka is in a valley so it's hotter than other Japanese cities - it will be a survival race," said Yamauchi, 33.
Significantly, Japan's Olympic marathon champion Mizuki Noguchi is not planning to chase the gold medal on home territory.
I can imagine there will be a lot of people dropping out (in Osaka), as in London
She believes even though the race is a year before the 2008 Beijing Olympics Games, there could be long-term problems recovering from it.
Yamauchi, a former Foreign and Commonwealth Office diplomat with a Japanese husband, said: "I think running a marathon there a year before the Olympics is a bit risky.
"But because I live in Japan, I shall be able to prepare properly for it. I think it will be a slow and tactical race.
"It will suit people like Deena Kastor (who broke the USA record in winning last year's London Marathon) who likes starting off slowly and coming through.
"I can imagine there will be a lot of people dropping out, as in London."
Yamauchi's sixth place secured her place in the British team for the championships from 25 August-2 September.