Lopetegui is now in Russian Federation with the Spanish squad, but will take over at the Bernabeu following the resignation of Zinedine Zidane.
Hierro said: 'We have no time to mourn. We've watched the videos for the next game and we need to use our brains, be coherent and, anyway, between now and Portugal there's not much room for change.
He will not be able to complete what he started in Russian Federation but his good work may not go to waste if Hierro can get Spain quickly back on track. "If not, the national team won't happen", he admitted.More news: Actor John Schneider released from jail in alimony dispute
'We have to be positive, opinions are not valid here, we have to turn the page, be positive, think about the players in the delegation and what we represent'.
Spain sacked Lopetegui on the eve of the World Cup after Tuesday's announcement he will join Real Madrid after the tournament.
Asked who would be taking over, he added: "We are going to touch as little as possible".
'When the president told me about the possibility, there were three options. "I know the circumstances and Julen's work has been fantastic and I wish him all the best", he said. I won't judge a club on how they act but, until a few minutes before, we were kept in the dark.More news: Farrah Abraham Arrested for Striking Beverly Hills Hotel Staffer
His appointment comes after Spain hastily called a press conference as reports emerged that Rubiales was outraged by the timing of Lopetegui's announcement. Plenty of countries have gone into tournaments in the past and had success despite knowing their manager will leave immediately afterwards.
However, despite many feeling that Lopetegui's connection with Real Madrid would cause friction within a already politically divided squad, the Iberian nation have gone and appointed a Real Madrid legend as their new coach in Fernando Hierro. I trust a lot in the talent and mentality of this team and I am sure that they can go far and fight for the title. When we know we will tell you. The favourite for the World Cup are without a manager.
Rubiales, the former head of Spain's players union who was elected as federation president last month, said he was forced to fire Lopetegui because he had been left in the dark by his coach and by Madrid.
Lopetegui's senior club experience is limited to 18 months at Porto, where he made headlines after beating Pep Guardiola's Bayern Munich side 3-1 in the first leg of their 2014/15 UEFA Champions League quarter-final.More news: Why Nike's World Cup boots have upset Iran coach Queiroz