Gerard Pique was booed as he trained with Spain for the first time since voicing his support for Catalan independence.
The Barcelona defender has admitted he is prepared to quit the Spanish team prior to the 2018 World Cup if requested to do so by the Spanish FA.
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Pique gave a tearful interview following Barcelona's 3-0 victory over Las Palmas on Sunday in which he described playing at an empty Nou Camp as the worst experience of his professional career.
"I go to play with the (Spanish) national team because I believe in democracy and there are a lot of people in Spain who don't agree with what has happened today," Pique told Spanish TV.
"The person who goes with the national team, isn't the most patriotic, you have to go and perform to your maximum. It's not a competition of patriotism; it's about going and giving all you can to win - that's how I understand it."
"If anyone in the federation believes I should not be there, I will step aside."
Pique has been an outspoken defender of the wealthy north-eastern Spanish region's right to self-determination and cast his vote in the independence referendum on Sunday morning.
Clashes left at least 92 people confirmed injured out of a total of 844 who needed medical attention, according to Catalan authorities.
"I am very proud of Catalonia and all of its people," an emotional Pique said. "Despite how much they are incited, and despite how much they (the Spanish authorities and security forces) want them to fall into the trap, they have demonstrated peacefully and sung loud and clear."