The versatile midfielder joined Barca from Arsenal in the transfer window, and even though he has admitted that it was not easy to say farewell to the English Premier League side, he did not need long to consider the offer.

"When Barca want you, you can't say no. A train like that only passes once in a lifetime and you have to catch it," Song told El Mundo Deportivo.

"I first heard about their interest in July. They talked with Arsenal, and Arsene Wenger came to tell me.

"It was difficult to convince Wenger and to say goodbye, because he helped me and my family a lot when I arrived at the age of 17."

The Cameroon international also looked ahead to the upcoming Clasico and said he would be more than ready if the coach needed him.

"I don't know whether I will play against Real Madrid," Song said.

"It is up to (coach) Tito Vilanova. We would obviously be stronger with (defenders) Carles Puyol and Gerard Pique, but I am ready for the task at hand.

"I've played against Cristiano Ronaldo before in the Premier League."

Barcelona host Real Madrid on October 7, but will take on Sevilla and Benfica before then.