London 2012: Van Commenee's Olympic warning to Dai Greene
UK Athletics coach Charles van Commenee has warned Dai Greene a repeat of his world title winning display may not win him the Olympic crown in London.
The Welshman in a time of 48.26 seconds in Daegu - but he is the 16th quickest in the world this year.
Greene in December and his 2012 best of 48.96 is a second slower than Puerto Rican Javier Culson.
"We won't know how strong the opposition is," said van Commenee.
"But even if he comes back to the form that he had in Daegu, that may not be enough."
World and Commonwealth champion Greene was named alongside fellow Welshmen sprinter Christian Malcolm, discus thrower Brett Morse and 400m hurdles rival Rhys Williams in the on Tuesday.
Head coach van Commenee has a target of eight medals - including at least one gold - at London.
Greene is one of the major home hopes alongside long-distance runner Mo Farah, former World Champion heptathlete Jessica Ennis, Beijing silver medallist triple-jumper Philips Idowu and world number one long-jumper Greg Rutherford.
The 26-year-old is aiming secure Wales its first athletics gold since Lynn Davies' long-jump title at the 1964 Tokyo Olympics, but Greene's form following his knee operation has been in indifferent.
He will race in the Diamond League meeting in Paris on Friday before completing his Olympic warm-up at the at Crystal Palace on 13 July.
"Dai has got time and is making good progress in training," said van Commenee.
"But let us see in five to six weeks for now. It looks feasible that he could hit top form."
Greene and Welsh 400m hurdles rival Williams start their Olympic campaign on the opening day of track and field events on 3 August at the Olympic Stadium. The final takes place on 6 August.
American Bershawn Jackson, the 2005 world champion and 2008 Olympic bronze medallist, has missed out on London qualification as the 29-year-old was beaten into fourth place in the 400m hurdles at the US trials with only the top three being selected.
Jackson, who had run the second fastest time this year, was beaten by surprise winner Michael Tinsley in a time of 48.33, with defending Olympic champion Angelo Taylor second and Kerron Clement, the Olympic silver medallist and two-time world champion, third.
Williams's season's best of 49.33 earned him European Championship glory at Helsinki last week and Olympic 400m hurdles qualification alongside Greene and Jack Green.
"Rhys is a very experienced competitor," said van Commenee, who watched Williams recover from a fall in the Olympic trial to securing his London place at the Europeans.
"He's a very determined man, he's not one who just switches on on the day of competition, he is switched on 365 days a year and is very intense.
"It takes a lot to beat him and he didn't allow it to happen in Helsinki. He's always a very positive force in the team, enthusiastic and supportive to other team members."