First and foremost, the decision, which was not backed by the Spanish government, will not have immediate consequences. Catalan clubs such as Barcelona, Girona or Espanyol will not be excluded from national competitions for now.
The process by which FIFA would recognise Catalonia as an independent state could last up to six years. For that reason, while the political situation is tense, circumstances pertaining to sport are to some extent relaxed.
Despite encouraging citizens to vote in favour of independence on October 1, Barcelona have stated repeatedly, namely through president Josep Maria Bartomeu, that they intend to stay in La Liga. For now, that will remain unchanged.
The situation could change if the Catalan Football Federation, currently linked to the Spanish FA (RFEF), opt to detach themselves from the national organisation and become a self-sufficient body. However, while it would not be as lengthy as FIFA's process to acknowledge Catalonia as an autonomous nation (six years), it would not have an effect on the current La Liga campaign.
If independence is claimed by the Catalan Federation, the future of the clubs from the north-east region would be completely different. The Spanish Government does not allow foreign clubs (except from those from the principality of Andorra) to feature in national sporting competitions.
Therefore, even though the procedure would be lengthy, if the Catalan Federation seconds the declaration of independence and cuts all ties with the RFEF, Catalan football would be destined to diverge from Spanish football. Furthermore, until FIFA recognises Catalonia as an independent state, the clubs would not have access to continental tournaments such as the Champions or Europa League.
To sum up, the declaration of independence will not affect Spanish football immediately. If the process of independence follows through, something that could not happen due to intervention from the Spanish government, Catalan clubs could be excluded from Spanish competitions in the upcoming years for belonging to a federation not associated to the RFEF. Barcelona, Espanyol, Girona and other Catalan teams may not be allowed to play in the Spanish La Liga or European competitions until FIFA, in a process that could drag on for up to six years, recognises Catalonia as an independent state.