Gold medal winning sprinter Darren Campbell believes Great Britain's athletes will find it difficult to match the success of London 2012 at this summer's Rio Olympics.
Britain won six athletics medals at the London Olympics with two golds from Mo Farah, one gold each from Jessica Ennis-Hill and Greg Rutherford, silver from Christine Ohuruogu and bronze from Robbie Grabarz.
Campbell, who is retired from athletics and now coaches sprinting at football clubs, said Team GB rely too heavily on a few star athletes, including Farah, Ennis-Hill and Rutherford.
The team has many talented younger athletes but Campbell said there is a lack of athletes who fall in the middle ground between the established names and the youngsters.
The 42-year-old said: "Rio is going to be a pressure-cooker atmosphere. It won't be like being at home and they're going to have to step up.
"I feel we have the talent, but only time will tell. I think it's going to be a lot more difficult.
"I think it's very easy to put all your eggs in one basket and things go wrong. I think there's a lot of pressure on a few athletes, rather than there being a lot of pressure on all the athletes.
"We've got a lot of talented young athletes, and then we've got a couple of athletes who are experienced, have been around a long time and know what it takes to win medals.
"Where's that middle area, those people that should make finals and maybe can pick up a medal that you just don't expect?
"Nobody expected me to win Olympic silver in 2000.
"You've got the established names, but it's those names where you go, 'Look, they always make finals, so it could be their time', it's those people I'm worried about.
"Have we got enough of those people who on the biggest stage could do something absolutely crazy?"
The British Championships, held this weekend at the Alexander Stadium in Birmingham, will be used to decide who makes it onto the team for Rio.
Campbell, who won a silver medal in 200m in the 2000 Sydney Olympics and gold in the 4x100m relay in Athens in 2004, said winning gold again will be a tall order for Ennis-Hill.
"This kind of puts it in perspective. No female British Olympian has ever retained their Olympic gold medal, so we are talking about Jess having to do something that no British female Olympian has ever done. That's for one gold," said Campbell.
"Mo's in exceptional form, so what we're hoping is that Mo Farah doesn't get injured and there could be two.
"If everything works out right - five, six medals, I think they've done very well."