Welsh 400m hurdler Rhys Williams said finishing fourth at the British Championships is a "big blow".
The event in Birmingham doubled up as trials for the European Championships in Zurich in August.
Williams (50.33) finished behind Niall Flannery (49.54 seconds), Tom Burton (49.78) and Sebastian Rodger (50.07) and now faces an anxious wait to see if he can defend his European title.
"It was awful," said Williams.
Bridgend-born Williams, who won gold in Helsinki in 2012 with a time of 49.33, is now relying on British selectors in order to defend his crown.
Flannery and Burton automatically qualify leaving the 30-year-old vying for the final selection spot, with Rodger and Dai Greene all contenders.
"I have not put myself in a good position and should have sealed the deal," said Williams.
"I am European champion but that was not how I planned to build up to these championships. Fingers crossed now with the selectors."
Flannery, Burton, Rodger and Williams have all met the European qualification time of 49.80.
Reigning Commonwealth champion Greene has not having not raced this season after undergoing three hernia operations in 2013.
The 29-year-old has until 13 July to reach the qualification standard time before British selectors make their final decision on who will go to Switzerland.
Williams, who along with Greene, has been selected by Wales for the Commonwealth Games in Glasgow, added: "It was a strange one.
"I don't know what happened there and have to look back at it.
"I can run much faster than that and it was awful and I am disappointed in myself.
"It is a big blow but I have to come back from it."