Will Clarke fears his dream of competing in a home Olympics could be over unless he wins a medal at the World Triathlon Series race in San Diego next month.
Brothers Alistair and Jonny Brownlee have already made the qualification standard for the London Games, meaning Clarke is realistically aiming for the last spot.
Clarke, from Cambridge, has consistently been the third best Briton over the past couple of years and won a medal at last year's race in Hamburg having also finished fourth in Kitzbuhel.
The British team will be selected after the world series race in Madrid at the end of May, but a phone call on Monday from Olympic men's coach Ben Bright left Clarke worried his efforts will not be enough unless he makes the podium in San Diego on May 12.
British Triathlon have made clear their aim is to win medals, and if they do not feel they have three athletes capable of doing so they have the option of picking a domestique to help the Brownlees, who finished last season ranked one and two in the world.
Clarke told Press Association Sport: "You need to be in the top three if you want to be selected or they'll pick someone who can help the Brownlees, and I need to be doing that in San Diego. Obviously finishing on the podium in the world series means you're one of the best in the world. Other countries are selecting from the top eight or top 10.
"(The phone call) did come as a shock. I've only been on the podium once in my career and a lot of other really good athletes won't ever get there. But that's the standard in Britain."
Clarke, who finished 14th at the Beijing Olympics four years ago, was the top British finisher in eighth at the opening world series race in Sydney earlier this month. He said: "I think it was the best that I was going to get. It's always a struggle to race really well at this time of year when you're used to peaking in our summer. I think I did a good job."
Clarke would be a leading candidate to fulfil the domestique role if he is not selected in his own right, but that would mean sacrificing his own ambitions, something he is certainly not prepared to resign himself to yet.
He said: "I'm in good shape and I've done everything I can. I've had the best winter's training of my life, I wouldn't change one day. Things like this can spur you on but it's very stressful in the meantime. You question whether you're good enough. I just need to try to relax and do the best I can."