Xavi described his return to Barcelona as "the biggest challenge of my career" after he was officially confirmed as the club's next head coach.

Barca announced in the early hours of Saturday that former Spain star Xavi had been appointed as Ronald Koeman's replacement at Camp Nou.

Club delegates travelled to Qatar this week to formalise the payment of the release clause in the 41-year-old's contract with Al Sadd, where he has been head coach for the past two and a half years.

Xavi's first senior coaching role in Europe will see him entrusted with steering Barca through one of the most difficult periods in their modern history.

Debts of more than €1.2billion meant the Blaugrana could not afford to sign Lionel Messi to a new contract or make any significant investment in the playing squad before this season, and results on the pitch have been concerning: they are ninth in LaLiga, having won only four of their first 11 games.

Xavi made 767 appearances for Barca in all competitions, a tally only surpassed by Messi (778), before retiring as a club hero in 2015 after winning his eighth league title and fourth Champions League.

However, he believes returning to the club at this time represents by far the toughest test he has faced as a professional.

Speaking to reporters before flying back to Spain, he said: "It's the biggest challenge of my career. I'm really happy, I'm coming home, coming back to Barca. It's a major challenge.

"I'm really grateful to Barca. They came to Doha, my contract was rescinded, there was a clause, and each of us has done our part. I'm really grateful to the club."

Xavi hopes his familiarity with some of Barca's more experienced players could serve as an advantage as he attempts to hit the ground running.

"The first thing to do is to speak with the players, to explain to them the ideas I have and to work a lot," he said.

"To coach friends is an advantage, it's a positive point. I know how they train and I know what they're like. I see it as an advantage."