De Gea made a high-profile blunder in Spain's 3-3 draw with Portugal by allowing a shot from Cristiano Ronaldo through his hands, which led to his status as number one keeper being called into question.
The Manchester United goalkeeper made his first save in the tournament in the 2-2 draw with Morocco in Spain's final group game and although he has not made any more costly errors since the game with Portugal, criticism has persisted.
"It is the most unfortunate position on the pitch but if you have seen David's games for Manchester United and his other games for Spain you'll be able to tell he is an outstanding goalkeeper," Thiago told a news conference.
"The media also need to take a look at themselves and realise what a great player he is. Look how many times he has been named best goalkeeper in the Premier League. He works like a bloody animal and the confidence we have in him is gigantic."
Spain meet hosts Russia in the round of 16 on Sunday after scraping to top spot in Group B with some underwhelming displays and some haphazard defending, highlighting how the sacking of coach Julen Lopetegui and replacing him with Fernando Hierro right before the World Cup began has unsettled the team.
Thiago did not deny that the shock dismissal of the team's long-time coach had affected the team although he said Hierro has had a calming effect, while insisting that Spain still trusted in their abilities.
"It has damaged us all because of how it happened but Fernando has taken on an important role and showed his level in games and in training sessions, he gives tranquility to us all and the confidence to approach games," added Thiago.
"We have faith that we can play to the level we have before. We have to improve in every sense, but we can start by having some confidence. We have everything we need. We need to trust in our teammates."
(Reporting by Richard Martin; Editing by Amlan Chakraborty)
