RFEF president Luis Rubiales announced on Tuesday Luis Enrique would replace Moreno for Euro 2020 and resume the role he left in June to take care of his daughter, who died in August of bone cancer.
But Moreno appeared upset with the way the change was handled as he refused to speak to the media after Spain's victory over Malta on Monday and reportedly left the dressing room in tears.
"If I went into my last few hours or even my last few days, I would only enter into a spiral of reproaches and recriminations. I'm not going to do it. I don't see any point," said Moreno.
"I have a clear conscience. It's impossible to thank everyone, but I want to say that I sincerely respect everyone and their opinions. I've always been a man of my word, that I wouldn't stand in Luis Enrique's way if he decided to return to coach.
"This is what I've done even though I've taken my exit. I wish him all the best because his joys will also be ours."
Moreno had overseen Spain finishing top of their qualifying group after an unbeaten campaign that included winning eight games out of 10 and scoring 31 goals. Spain won four and drew two of his six matches officially in charge.
Rubiales rejected accusations of dishonesty on Tuesday and Moreno has said he remains grateful to his former employers.
"I want to thank all the members of the Spanish Football Federation for the treatment I received during my time with the national team. I've felt loved and respected," Moreno continued.
"My experience with the national team started and finished in the same way, with a bitter-sweet feeling. It's now about looking forward and facing new challenges as a coach in my passion, which is football."