WATCH: Gerard Pique jeered by Spain supporters after Catalonia independence referendum

Barcelona's Gerard Pique was booed and jeered as he trained with the Spanish national side on Monday.

Pique had voted in Catalonia's independence referendum on Sunday morning, despite Spanish authorities deeming the vote illegal. Spanish police clashed with voters in the region throughout the day, confiscating ballots and, in some cases, violently removing activists. Hundreds were left injured. Barcelona asked La Liga to postpone their league meeting with  Las Palmas in the afternoon - a request that was rejected. As a result, the game was played behind closed doors at the Camp Nou stadium, with only press permitted to watch the game.

"I am very proud of Catalonia and all its people," Pique told reporters in an emotional post-match interview.

"Despite how much they are incited, and despite how much they (the Spanish authorities) want them to fall into the trap, they have demonstrated peacefully and sung loud and clear."

Pique, part of Spain's World Cup-winning squad in 2010, also added that he would retire from international football if his stance on the matter was regarded a problem.

Clearly, as the video below shows, it does appear to be a problem for many of those in attendance at an open training session in Madrid...

https://twitter.com/EJCASTELAO/status/914910508289060865