La Roja were beaten 2-1 by Serbia in the second leg of their playoff on Tuesday evening, with the defending champions failing to qualify for the finals as a result.
"It is not the time to dwell on that in the heat of the moment. I'll have to think about it, reflect on things and see what conclusions we draw," he told reporters.
"It's a shame we didn't qualify and that we met Serbia in the play-offs, as they are a great team, but the format is the same for everyone and we knew what it would be like before we started the qualifiers.
"I'd like to repeat that sometimes in football the best team does not always win. The players are broken."
Celades took charge of Spain's Under-21 side earlier this year.