SOCHI, June 15 -- Group B heavyweights Spain and Portugal will kick off their World Cup campaigns here on Friday night. Xinhua takes a look at four key issues likely to dominate the agenda when the Iberian giants go toe-to-toe in the Fischt Stadium.

1) Will off-field matters have an effect?

Both teams go into the game with off-field problems, but while five members of the Portugal squad are in conflict with their club Sporting Lisbon, Spain have taken the unprecedented step of sacking coach Julen Lopetegui just two days before the game, after it was revealed that he had been negotiating with Real Madrid without the prior knowledge of the Spanish football association. Former international defender Fernando Hierro will take temporary charge of the team in his place. Both Hierro and Spain captain Sergio Ramos insisted the dressing room remained united after the chaotic events, but just how settled they are will only become clear once the ball starts rolling in Sochi.

2) What changes will Hierro make?

With just two days to prepare for the match, Hierro hasn't had much chance to introduce any changes to the system that worked so well for Lopetegui and his predecessors Vicente del Bosque and Luis Aragones. Lopetegui had shown a willingness to introduce a more direct style into the Spanish game during his two years in charge, but the Spanish still use a high-pressing game and then look to pass their way through their rivals, meaning patience will be vital in the game.

3) Who will be the key men?

Whenever Portugal are in action, most of the focus is on Cristiano Ronaldo, but Portugal's success in the 2016 European Championships was mainly down to their rock-solid defense. Few Portuguese players know Spain better than Pepe and his aggression and power is vital at the back, while for all the talk of Ramos, Costa and Andres Iniesta, midfield lynchpin Sergio Busquets is the man who pulls the strings for Spain, and if he plays well so will his side.

4) The fallout

A win for Spain will put a temporary end at least to their institutional crisis and allow Hierro to prepare for the theoretically easier tests against Iran and Morocco. However, a draw or a defeat will set alarm bells ringing in the Spanish press and a search for scapegoats would further complicate the atmosphere ahead of the next two matches.

Portugal, meanwhile, will remember that their Euro 2016 campaign hardly got off to an inspiring start, and yet they still ended up as champions.

Winning your opening World Cup match is always important, but in this case, it is probably even more so for the Spanish.