Williams suffered the injury at the Welsh Championships
Welsh 400m hurdler Rhys Williams is out of the Beijing Olympics after suffering a stress fracture to his right foot.
The six-week recovery period rules him out of the Olympic trials in July.
Williams, 24, the son of ex-Wales and Lions rugby star and international sprinter JJ, said: "I'm gutted, but it's not the end of me."
Williams suffered the injury in Sunday's Welsh Championships at Swansea, his first appearance since a similar injury blighted his 2007 hopes.
He added: "This has made me more determined. You have not heard the last of me and I promise to be there doing my thing for Wales.
"Up to last month I was struggling in training, but in the last month things seemed to be going well.
"But unfortunately I ran on the weekend and cracked a bone in my foot and I have to take the rough with the smooth.
"It went in the middle of a race. I just felt a bone crack. It's unfortunate."
JJ said: "After all the injuries he's had he was totally fit and feeling great, so he decided to have a run out on Sunday.
"The Welsh Championships was a fairly low key event. He entered the 200m and breezed through the heat.
"Thirty minutes later he ran in the final, and after 20m cracked something in his foot.
"Tests have revealed it is a stress fracture in his right foot. He's out for six weeks. He'll miss the trials in mid-July. So there is no way he's going to the Olympics. He's devastated.
"He's looking to come back sometime in August and salvage something from the season."
Williams won 400m hurdles bronze at the 2006 European Championships and silver in the 4x400m relay.