After a dismal defence of their World Cup crown in Brazil and a friendly defeat to France in Paris last month, Spain's bid to rebuild as they seek a third straight continental title was rudely interrupted by Thursday's shock 2-1 defeat against Slovakia in Zilina.
Toothless in attack and shaky in defence, Vicente del Bosque's side slipped to their first reverse in qualifying for the World Cup or European Championship in eight years and an unbeaten run of 36 qualifiers came to a shuddering halt.
Captain and goalkeeper Iker Casillas was at fault for Slovakia's opening goal, flapping at a swerving Juraj Kucka free kick in the latest of a series of blunders, while Brazil-born forward Diego Costa has still not scored in six appearances for his adopted country.
Costa had a superb season with Atletico Madrid in 2013-14 and has been in electric form for new club Chelsea this term but has yet to click into gear on the international stage.
Spain desperately need a reliable goalscorer to replace David Villa, who has retired from the national team after netting a national record 59 goals in 97 appearances.
"He (Costa) is not having much luck with us but he is the top scorer in the Premier League and last season he got a lot of goals for Atletico," Del Bosque said on Friday.
"Maybe it is not helping him that he is so desperate to please and do things well," he said, adding that he was planning to make the odd tweak to the team but not change much from the Slovakia game.
Paco Alcacer, Villa's successor both for his club Valencia and as a recent addition to Spain's forward line, netted the equaliser off the bench on Thursday and could partner Costa in attack against Luxembourg.
"The important match is not the one in the recent past but the one on Sunday," Alcacer told a news conference on Friday.
"The Slovakia game was rough but Sunday's will be a means of giving ourselves a lift," added the 21-year-old.

Ranked 127 by FIFA, Luxembourg are unlikely to present anything like the same challenge as the battling Slovakians.
They have lost all four of their previous meetings with Spain, all friendlies, without finding the net and were beaten 3-2 away to Macedonia on Thursday to leave them joint bottom of the group with one point from two matches.
Luxembourg coach Luc Holtz, who played in his nation's most recent game against Spain, a 1-0 win for La Roja in June 2000, said his players had deserved more from the Macedonia game.
"The first 15 to 20 minutes were very hard for us, but after our first goal we were the better team," Holtz told a news conference.
"We were very unlucky at the end because Macedonia scored in the dying minutes," he added.
"We will try our best in all of our games, but it will be difficult if we concede in the final minutes,” he said.
Slovakia lead Group C with a maximum six points, with Spain, Ukraine and Macedonia level on three and Belarus also on one.

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