Friday's 1-1 draw with Group I's bottom side Finland, coupled with a 3-1 win for France against Georgia, left them two points adrift of Didier Deschamps' men in the section.
It may be a little soon to start panicking, but Spain can ill afford to lose at the Stade de France -- do so and they will be five points off top spot with just one automatic berth at next year's finals in Brazil up for grabs.
Indeed, some in Spain are even beginning to entertain the possibility that a defeat on Tuesday could lead to them missing out on a play-off place.
Only the eight best runners-up will get a second chance to qualify in the two-legged play-offs, with the poorest performing runner-up missing out.
Such a scenario seems highly unlikely, but it is no exaggeration to say that things have not been this bad for Spain in a long time.
Having won three consecutive major international tournaments, Spain have become accustomed to winning, so failing to beat opponents as limited as Finland calls into question the methods that have worked so well in recent years.
Spain utterly dominated possession against the Finns at Gijon, with even their central defensive pairing of Gerard Pique and Sergio Ramos spending most of the evening in the opposition half of the field.
But they lacked the imagination and the width required to break down the visitors' defensive wall, and were too often restricted to shots from long range.
Coach Vicente Del Bosque tried several permutations in attack, from Cesc Fabregas in the role of a false nine, to Cesc and David Villa together and the introductions of burly Sevilla striker Alvaro Negredo and Chelsea's Juan Mata.
They couldn't kill the game off after Ramos' headed opener early in the second half and were made to pay when Teemu Pukki equalised late on.
Following last October's 1-1 draw with France in Madrid, Spain have now gone two successive competitive home games without winning for the first time since the 1982 World Cup finals, a statistic that conjures memories of older, far less glorious times.
"Teams have found a way of playing against them," observed France midfielder Blaise Matuidi. "Now it's up to us to do the same."
The prevailing opinion in the Spanish media is that Del Bosque's team were over-confident and allowed thoughts to drift towards France before Finland had been put to bed.
The loss of David Silva due to suspension and flying left-back Jordi Alba to a thigh problem has provided further cause for concern.
But Del Bosque, who has now passed Laszlo Kubala's record of 68 matches at the helm, is nothing if not a reassuring presence and is not about to push the panic button just yet.
"There are still four games to go and it is still in our hands," he said.
"We must not be pessimistic. We will be going to France to try and win."
There is good reason for Del Bosque to be optimistic. Like Finland, France may have snatched a draw in Spain, but they will surely not be so defensive in their approach on home soil.
"They are well within their rights, but we never imagined they would be so defensive," the Spanish coach said of Finland. In contrast, France will be compelled by their demanding support to attack.
"I don't see myself telling my team to just defend," said France coach Deschamps.
That philosophy is admirable, but could play right into Spain's hands, especially if key midfield duo Xavi Hernandez and Xabi Alonso both return after missing Friday's match.