The Swedish striker suffered a minor broken bone in his left hand while playing in a friendly for Inter Milan against Chelsea last week.
Begiristain said Ibrahimovic was 'the best option that we could find in the world to replace (Samuel) Eto'o', who has controversially been off-loaded to Inter in part exchange for the Swede.
Barca have paid Inter around 45 million euros ($63.94 million) for Ibrahimovic -- top scorer in the Italian league last season -- plus Eto'o and the loan of Alexander Hleb for one season.
Ibrahimovic, 27, told the media: 'I am not the substitute for Eto'o. I am something different. I am here to work, and this is a dream for me. I am pleased that this agreement has been made.'
He added that 'to play for Barcelona is a great honour ... I hope to become a better player here.'