De Gea was at fault for Portugal’s second goal as he failed to save Cristiano Ronaldo’s speculative shot from the edge of the penalty area in the 44th minute, as the ball found its way into the back of the net.

"The mister [Spain head coach Fernando Hierro] is with me and the whole team - I am calm," de Gea said.

"It is a mistake that can happen to any goalkeeper. A difficult ball. (We need) to continue training and to do things well in an important game against Iran because we have strong options to win..

The 2018 FIFA World Cup kicked off on Thursday and will continue until July 15, with a total of 64 matches set to be played at 12 stadiums across 11 Russian cities.

Spain will face Iran in Kazan on June 20 before taking on Morocco in Kaliningrad on June 25 in their other two Group B matches.