MADRID • Two of the World Cup's leading contenders will meet in Madrid today 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 partner Lionel Messi, with the two-time winners again boasting an embarrassment of riches up front, while showing little indication how to deploy them.

The supporting trio of Gonzalo Higuain, Sergio Aguero and Angel di Maria could reunite in Russia in June but they have disappointed together before.

Meanwhile, Paulo Dybala faces a fight for inclusion after being left off Sampaoli's latest list. 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 Messi, who has been struggling with pain in his hamstring and adductor.

"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, Alvaro Morata and Iago Aspas jostle for the lead striker's role.

Costa was the clear favourite after starting five of Spain's opening six World Cup qualifiers but his fallout 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 Rodrigo 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 LaLiga 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 their campaign against Portugal on June 15, while Morata still has three months to spark a revival.

But it is Valencia striker Rodrigo who has momentum, on the back of two consecutive starts and a sharp finish in the 1-1 draw against Germany on Friday. He now has three goals in five international matches.

"These games are important to know what we will find later in the World Cup," Spain captain Sergio Ramos said of the match today.

AGENCE FRANCE-PRESSE