Hampshire-based runner Louise Damen's hopes of competing at the 2012 Olympics have been dented after she dropped out of the Yokohama Marathon on Sunday.
Damen dropped out midway through the race with searing temperatures of 23C hampering her progress.
And she suffered a further blow with news she has slipped to fifth in the GB rankings with only three places available for the London Games.
"I always knew it was going to be tough," Damen told BBC Radio Solent.
Oxford-born athlete Mara Yamauchi ran two hours 27 minutes and 24 seconds on Sunday - comfortably inside the Olympic qualifying time of 2hr 31min.
That saw her move to second in the British rankings behind Paula Radcliffe, leaving Jo Pavey, Claire Hallissey and Damen fighting for one spot.
And Damen, a 28-year-old teacher, says she had hoped to improve her personal best before being forced out of the race.
"Unfortunately we had some unexpected weather in Yokohama on Sunday and it didn't go to plan," said Damen.
"Originally we planned for weather a lot like we've got in Britain at the moment so about 12 degrees which is ideal weather for running a marathon.
"Unfortunately it was 25 degrees and very humid and I was totally unprepared for that.
"Had I known it was going to be hot and humid then that may have affected my choice of marathon. I wasn't prepared for it and I struggled in the heat if I'm honest."
Damen admits she faces a fight to get into that GB team and will likely need to impress at next year's London Marathon if she is to make it into the Olympics.
"I always knew it was going to be tough and I'll have to go to the London Marathon and run well there," added Damen.
"To be honest I was going to have to do that anyway and I knew it was going to be tough to make the team. I'm going to have to have the run of my life in London and hopefully I can make the team."