Jenny Meadows' participation in the Olympics is in doubt after she was ruled out of this weekend's trials in Birmingham.
The 800 metres runner has not raced at all this year because of an Achilles injury.
The 2009 World Championships bronze medallist is still recovering from the problem and will now need to rely on the discretion of the selectors to be awarded the third and final place on the team for London.
Jeanette Kwakye, a 2008 Olympic finalist in the 100m, will also miss the trials due to an Achilles and ankle injury.
The pair's withdrawal is worrying news with the Games six weeks away and comes just a day after Hannah England, the World Championships silver medallist over 1500m, announced she too would miss the trials after suffering a spike to her Achilles in a race in Holland three weeks ago.
Meadows, 31, still plans to run at the European Championships in Helsinki next week where she will look to prove her form and fitness.
But two athletes, British number one Marilyn Okoro and Emma Jackson, have already run the Olympic 'A' standard of one minute 59.90 seconds this year and, with the top two finishers at the trials gaining automatic selection for London, providing they have that standard, the pressure will be on Meadows to perform in the Finnish capital.
"I am gutted to be missing out on the Aviva Olympic Trials, but we always knew it would be a race against time to be fit enough," the Wigan athlete said.
"Every day of my recovery is like a week so the extra few days ahead of Helsinki will make a big difference to the injury and ensure I am able to go out and compete and demonstrate my fitness ahead of selection for London 2012."
Meadows is more than capable of going quicker than Okoro's 1min 59.33secs in Helsinki - in her last race in Zurich last September she ran 1m 58.92s - but the women's 800m is one of the most competitive events at the trials, with Jemma Simpson, a 1:58 runner at her best, also in the mix.
Kwakye, who has a best of 11.68 this year to sit well down the British rankings and has not yet decided on her participation in Helsinki, is also determined to compete in London.
She said: "I have been working with the UKA medical team at Lee Valley and on their advice and in consultation with my coach Michael Afilaka we have decided to miss the trials.
"We will reassess the injury on Monday in relation to the European Championships.
"I am eligible for selection for the Games and am still determined to be fit and ready for competing in my own backyard in Stratford."
Abi Oyepitan and Laura Turner have run the 'A' standard for the 100m this year.
