Spain slumped to a disappointing 2-1 loss in Zaragoza that leaves it trailing Portugal by two points in UEFA Nations League Group A2 heading into the last game.

That final group match is on Wednesday (AEST) as Spain prepares to face Portugal in Braga, with Fernando Santos' side securing a 4-0 win over Czech Republic on Sunday (AEST).

La Roja did not muster a single shot on target until Jordi Alba's 55th-minute equaliser at La Romareda, and Luis Enrique could not hide his disappointment at the display.

"Losing is always something that hurts. It has been a pity, but we must value Switzerland, who from the beginning caused us many difficulties," the coach said.

"In the first half, it was the worst of my time as coach. [Then] we have badly defended the corner of their second goal.

"In the second half we improved. We have tried until the end. The key game is Portugal. We will go to Braga to win."

The manner of Sunday's (AEST) loss clearly perturbed Luis Enrique, understandable given the FIFA World Cup starts in less than two months.

Yet, he is adamant he does not need to re-evaluate his faith in the squad because of one result.

Asked if the game generated doubts in relation to the FIFA World Cup, Luis Enrique replied: "No doubts.

"Obviously it's better to go to Qatar on a winning streak, but I have full confidence in the team. I have seen many players in the first half who have been more imprecise than ever, but the opponents are good, they know how they play.

"But everything doesn't always go well, when you don't have a good day, this happens.

"A victory against Portugal would be the perfect way to reach the World Cup. We have drawn three times with them and now we will go there to win."

Portugal only needs a draw on Wednesday (AEST) to seal its place in the UEFA Nations League Finals for the second time.