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European champions are tested in Serbia, Portugal play at home.
Premiere of the Nations League with European champions Spain testing Serbia and Portugal hosting Croatia.
Two more teams who have been on the pitches in Germany in the last major European football competition will play each other.
Denmark will face Switzerland at home, with the hosts having a slight advantage in the odds due to their home ground.
However, Switzerland proved to be a very good team at the EURO and were one of the pleasant surprises.
Spain will attempt to start on the right foot at a difficult home ground. Yamal's formidable side, who won Europe two months ago, aim to start their Nations League campaign on the right foot. They will face the always dangerous and inconsistent Serbia.
The Serbs disappointed at the EURO in Germany and in no way lived up to their high expectations. However, they have a chance to entertain impressions against the best team in Europe.
Spain are the favourites, but they will have to sweat it out to confirm their title.
The most important game will take place in Portugal, with the Iberians hosting Croatia.
Both teams failed to fulfill their lofty goals at the last EURO, having bid farewell to the competition relatively early. Portugal in particular had aspirations all the way to winning the trophy.
In the opening match of the Nations League, both teams are optimistic to start with a win. Portugal will look to capitalise on their home ground and the formidable quality of their players, and Croatia will look to use tight defence and attacking efficiency.