London 2012: Dai Greene's Olympic build-up hurt by surgery
Dai Greene's Olympic preparation has been hampered as the 400m hurdle world champion underwent knee surgery during the winter, it has been revealed.
The Welshman has begun his Olympic year with disappointing times as Greene, one of the favourites for gold at London 2012, is 14th fastest in the world.
Greene's season's best of 48.96 seconds is more than a second slower than the 2012 quickest Javier Culson.
"He has had a tough winter," Greene's coach Malcolm Arnold told BBC Sport.
"He didn't say much about it but he had to have some knee surgery just before Christmas which he has been rehabilitating out of since Christmas.
"He has had two races which have both been of the required Olympic A standard but not quite a quick as we had hoped for."
The European and Commonwealth champion opened his season with a in May before running 0.02 seconds slower in the , finishing fourth in a race where winner Puerto Rico's Culson ran a season's best of 47.92 seconds.
Greene will compete at the Olympic trials and AAA Championships in Birmingham, starting on Friday, and is expected to complete his London preparations by racing in the Diamond League meetings in Paris on 6 July and Crystal Palace on 13 July.
Should he add an Olympic title to his world, Commonwealth and European golds, Greene would become just the fifth British athlete alongside Linford Christie, Daley Thompson, Jonathan Edwards and Sally Gunnell to win all athletics' major medals.
The 26-year-old is also bidding to become the first Welsh Olympic champion in track and field since long-jumper Lynn Davies won gold at the Tokyo Games in 1964.
And renowned coach Arnold feels Greene is recovering well from December's knee operation.
"In this last week, he has had the best weeks training I have ever seen him have," said Arnold.
"I think he is coming good at the right time."