Tim Benjamin has withdrawn from the Wales team for the Commonwealth Games in Melbourne this March. Britain's leading 400m runner, who would have been a realistic gold medal hope if fit, has seen his training blighted by a persistent groin injury.
"I have only been able to train sporadically at 50% for the past two months," said the 23-year-old.
"Although I am aerobically fit I will not have enough time to do the speed work to compete at the top level."
Benjamin came fifth at the World Championships in Helsinki last year, before again lowering his personal best to 44.56 seconds en-route to second place at the IAAF World Athletics Final.
The Belgrave Harrier now has four months to prepare for the European Championships.
His absence from Melbourne will also be a huge blow to the Wales 4x400m relay squad, which came so close to beating England at the Manchester Games four years ago.
Welsh Athletics director of coaching, Phil Banning, said: "To lose such a talented athlete from the squad is a massive blow and our best wishes go out to Tim at this time.
"We are confident that he is getting the full support necessary to ensure that his recovery process is swift and that he will be back to compete against the best in the world later this year."
Wales 2006 Commonwealth Games athletics team:
Men:
100m: Christian Malcolm.
200m: Christian Malcolm.
400m: Gareth Warbuton.
400m hurdles: Matt Elias, Rhys Williams.
4x400m relay: Iwan Thomas, Gareth Warbuton, Matt Elias, Rhys Williams.
1500m: James Thie.
5000m: Chris Davies.
Long jump: Stephen Shalders.
Triple jump: Stephen Shalders.
High jump: Robert Mitchell.
Pole Vault: Scott Simpson.
Women:
400m: Catherine Murphy.
800m: Hayley Tullett.
1500m: Hayley Tullett, Natalie Lewis.
Long distance: Catherine Dugdale.
High jump: Julie Crane.
Hammer: Carys Parry, Leslie Brannen, Laura Douglas.
Discus: Phillipa Roles.
Marathon: Tracey Morris.