The shirt was forced on the 23-year-old by Barca defenders Gerard Pique and Carles Puyol as Liverpool goalkeeper Pepe Reina announced "the future of Barcelona" to the crowd.
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"It was a day of celebration and anything goes," Francesc Fabregas told COM Radio.
"If anyone misinterprets it, they have to see that it was part of a celebration.
"Cesc has it very clear what Arsenal has been and is for him.
"He is super grateful to them and it has never crossed his mind to do something wrong towards them.
"Cesc said what he wanted to do [sign for Barcelona] the day after the end of the league so that Arsenal had time to react.
"It would have been nasty to say it today, when they are almost on the verge of starting the pre-season.
"But he always did so thinking about Arsenal. It remains to be seen how everything turns out."
Fabregas made four substitute appearances for Spain during their World Cup campaign, assisting Andres Iniesta’s winner in the final against the Netherlands on Sunday.