Spain - Two of the World Cup's leading contenders will meet in Madrid on Tuesday but neither Spain nor Argentina have yet settled on a forward line for this summer.
For Argentina and Jorge Sampaoli the question is who best to stir Lionel Messi, with the two-time winners again boasting an embarrassment of riches up front, while showing little indication they know how to deploy them.
The supporting trio of Gonzalo Higuain, Sergio Aguero and Angel di Maria could reunite in Russia but they have disappointed together before, when all were younger and arriving in better form.
Meanwhile, Paulo Dybala, one of the game's most exciting young forwards, faces a fight for inclusion after being left off Sampaoli's latest list, and Mauro Icardi is expected to find his 26 goals for Inter Milan this season insufficient to make the squad.
Argentina may have to continue their search at the Wanda Metropolitano without their key component as Messi has been struggling with pain in his hamstring and adductor.
He trained on Sunday but is unlikely to be risked.
"Spain already has its team and knows how it will play at the World Cup," Sampaoli said. "We have to find that certainty."
But for Spain and Julen Lopetegui, there is also uncertainty in the final third where it is less a question of too many choices but too few as Diego Costa, Rodrigo Moreno, Alvaro Morata and Iago Aspas all jostle for the lead striker role.
Costa was the clear favourite after starting five of Spain's opening six World Cup qualifiers but his fall-out with Chelsea, that led to five months stewing in Brazil, prompted Lopetegui into a rethink.
"The coach was always very clear with me," Costa said on Friday.
"He told me: 'If you do not play, you cannot come'. But he also told me that when I played again, if I did it right, I had the doors open."
In the last seven games, four of them qualifiers, Costa is yet to start while Morata has been picked twice and Moreno three times.
It would seem too late now for Aspas but, unlike Morata, he is in the current squad and has the benefit of form, having hit 16 goals for Celta Vigo in La Liga this season, more than any other Spanish player.
Costa, however, is back playing for Atletico Madrid, which makes him the likeliest choice when Spain open up against Portugal on June 15, while Morata still has three months to spark a revival.
"Morata still has a lot of possibilities to go to the World Cup," Lopetegui said last week.
But it is Moreno who has momentum, on the back of two consecutive starts and a sharp finish in the draw against Germany on Friday, which means he now has three goals in five international matches.
"It has been a great night both individually and collectively," Moreno said after his goal against Germany. "The next squad is the most important and everything will depend on what happens from here to the end of the season."
There is still time, but the selection against Argentina will be instructive given they represent Spain's last elite test, with Tunisia and Switzerland their final friendlies in June.
Lopetegui has now overseen 17 matches without defeat and a bold performance against the world champions has increased the sense his team are ready to challenge.
Victory over Argentina, regardless of who he picks up front, would swell that confidence further.
"These games are important to know what we will find later in the World Cup," captain Sergio Ramos said. "We have our feet on the ground and we know there is much to improve. You can never be complacent, only convinced of what you do, and we are. We are on the right way."