Former Spain and Real Madrid captain Hierro, who moves from his role as the team's director of football, was set to be presented to the press at the Krasnodar Stadium later on Wednesday before getting to work in his new post.
Lopetegui signed a three-year deal with the UEFA Champions League winners on Tuesday but was poised to lead the La Furia Roja to the 2018 FIFA World Cup in Russian Federation.
"We wish him the greatest of luck", the federation's president, Luis Rubiales, told reporters at the team's World Cup training headquarters, per the Guardian.
And on Lopetegui's replacement, Fernando Hierro, he believes he "is a well-prepared person to take charge of the national team".
Lopetgui took over the Spanish team after the 2016 European Championship that had been on the decline after its streak of winning the Euro in 2008 and 2012 and the 2010 World Cup.More news: Kate Middleton takes George and Charlotte to watch William in polo match
Rubiales had been riled by being told of Lopetegui's decision to take the Real job just five minutes before it was made public.
"I came from Moscow because this issue is more important, and we had to react".
Lopetegui was announced as the new Real Madrid boss on Tuesday, taking over from departed Zinedine Zidane after the tournament.
Spain play their first Group stage match against Portugal on Friday. "We are left in a very hard situation", he said. Lopetegui, while he has been with us, has done an impeccable job.
The World Cup in Russian Federation starts on Thursday.More news: Tea towels can cause food poisoning
"I have spoken with the players and I can guarantee that the new technical team will do everything they can".
Lopetegui was dismissed on Wednesday by Spanish football chiefs who were left furious by his decision to join Real Madrid ahead of the tournament. "We all know what this means and our responsibilities". "We have to think about what is best for the entity, for the federation and the team, and from this afternoon we will all be together to go forward".
"I feel very close to the players and to Julen", declared Rubiales.
'I do not feel betrayed, the problem is how things have been done with the total absence of participation of the Spanish Football Federation, that is something we can not ignore, Lopetegui is an impeccable professional but the process is important. "It may look like a weakness now, but with time this will make us stronger". I admire Julen very much, I respect him very much. "They've shown me they are "all in" here and I have no doubt they'll give their all whatever happens", he said.More news: Federal Bureau of Investigation agent who shot club patron while breakdancing charged with assault