Spain coach Vicente del Bosque said he is wary of facing Croatia at Euro 2016 after they were drawn together in Group D along with Czech Republic and Turkey.
Two-time defending champions Spain will attempt to be the first nation to win the tournament three times running, but Del Bosque said they must overcome a "extraordinarily tough" group.
"We will go there with the aim of winning the Euro for the third consecutive time," he said. "It would be fantastic for Spanish football. No one has ever achieved this. However, we know we will have to face extraordinarily tough opponents."
Del Bosque cited the qualifying campaign of Czech Republic and Turkey, both of whom finished above Netherlands to qualify, as proof of the group's strength.
"We've drawn two teams who played in the same group as the Netherlands and eliminated them -- Turkey and the Czech Republic," Del Bosque said.
"Then we have to face Croatia, who are very strong and who, for me, are among the strongest teams at this tournament. They have excellent players. It will be very difficult for us."
Croatia coach Ante Cacic admitted Spain would be favoured to top the group and his side had their work cut out for them.
"I can say that Spain, as reigning champions and given they still have a lot of quality players, are the favourites in the group," Cacic said.
"And Croatia, Czech Republic and Turkey are three teams who will do everything to continue in the tournament. So I think it will be very interesting.
"To get through this group would already be a significant result. After that, during the knockouts, it will depend on the draw."
Czech Republic coach Pavel Vrba welcomed the opportunity to face Spain at the beginning of the competition.
"Maybe we have a slight advantage, because we start against Spain -- the decisive matches against Turkey and Croatia will come later," he said.
Goalkeeper Petr Cech said playing a long club season on multiple fronts could affect many of Spain's top players.
"It may look tough on the paper, but it will be played at the end of the season when players' form will be crucial," Cech said. "It would be foolish to give up hope before it has even started."
Turkey coach Fatih Terim said his team wouldn't shy away from competing against the mighty La Roja.
"We will not have fear from anyone and try to enjoy our football on the pitch," he told UEFA. "There's no need to talk about Spain. The team is full of stars."