Pep Guardiola addressed a pro-independence rally in Catalonia on Sunday to present the case for a referendum on the issue.
The Manchester City boss read out a manifesto in Catalan, Spanish and English to the 40,000-strong crowd assembled at Montjuïc as he threw his hat into the ring.
On Friday the Catalan government announced it would be holding a referendum on the issue in October but the response from Madrid was that this would not be legal and it would not be allowed to proceed.
“We have tried on 18 occasions to reach an agreement on a referendum and the answer has always been no,” Guardiola said.
“We have no other option but to vote. We call on the international community to support us and on democrats the world over to help us to defend the rights that are threatened in Catalonia, such as the right of freedom of expression and the right to vote.”
Catalonia held an unofficial referendum in November 2014 in which 80% voted for independence and there have been suggestions such a split would have massive implications for La Liga.