Are the wheels coming off at Barcelona ?

That's the question in Catalonia as the Spanish champions suffered a body blow on the eve of the new season with the news that manager Tito Vilanova was stepping down .

Barcelona president Sandro Rosell confirmed Vilanova's departure is related to his ongoing battle with cancer, saying his treatment precluded him from continuing in the role.

"This is a difficult blow for the club to overcome," said Rosell at the hastily-called press conference. "But Barcelona have overcome difficult blows before."

Vilanova missed two months of last season after needing surgery and treatment to remove a tumor on his salivary glands. Vilanova was first diagnosed with cancer in 2011.

Barcelona will announce Vilanova's replacement next week. Local reports speculate that Rubi, only a week into his role after leading second-division side Girona to a fourth-place finish last season, would be an interim caretaker. Other reports suggested that Argentine coach Marcelo Bielsa would be offered the position.

Barcelona's players reacted with shock, with Jordi Alba telling the Spanish media that there had been no warning, and expressing sadness. "The most important thing is Tito's health." Other Spanish stars took to social media, with Liverpool's Pepe Reina and the Los Angeles Lakers ' Pau Gasol sending Vilanova get-well messages:

El fútbol es efímero igual q sus triunfos y derrotas.Toda mi fuerza para Tito Vilanova y su familia!!Animo!!este partido tb lo vas a ganar!

-- Pepe Reina (@PReina25) July 19, 2013 The first and most important thing in life is health. My best wishes to Tito Vilanova in this difficult moment. #ànimsTito #GetWellSoon

-- Pau Gasol (@paugasol) July 19, 2013 The coaching shuffle leaves Barcelona in a lurch after a season that saw them win the league, but tumble inelegantly and painfully out of Europe, partly due to Vilanova's absence. But it also means a clean break with Barcelona's recent - and winning - past.

Vilanova had provided continuity after the departure of Josep Guardiola, playing the same elegant style of soccer that had seen them crowned as the consensus best club side in the world. Barcelona also provided the nucleus of Spain's World Cup and European championship squads. All those games, added up, took their toll: last season, in many ways, felt like the exhaustion had finally caught up with Barcelona and the curtain was coming down on an incredible era.

In attempt to fix that this season, Barcelona went out and captured one of the world's great young players in Neymar, a true attacking threat who should link up beautifully with star Lionel Messi. But now, Barcelona don't have a teacher in Vilanova, and job one will be going out and acquiring someone who can make their world-class attackers play in harmony.

Other issues - including a leaky defense - have yet to be solved as well. Barcelona have been frustrated in their attempts to reinforce their defense, as wealthy Paris Saint-Germain have twice beaten them to the punch on Thiago Silva and Marquinhos.

Then there are the exits, with one player out the door and another seeming to be heading to England. Thiago Alcantara moved to Bayern Munich after the German champs triggered the midfielder's unusual get-out clause. The transfer, a relatively cheap one at $30 million, is great business for Bayern and awful for the Spaniards, who had bizarrely added a guaranteed playing time clause into Thiago's contract. When they didn't come close to meeting it, he was free to leave. Cesc Fabregas may be next: Manchester United is said to be close to acquiring the former Arsenal star in a move said to be valued at $40 million, a sum Barcelona will have a hard time turning down after splashing out $75 million on Neymar alone.

Both moves have shaken Barcelona fans for reasons that have everything to do with ego. Barcelona simply don't like being a club that gets raided - they'd prefer to do the raiding themselves, thank you very much - so it raised an additional shiver this week when PSG said they were perfectly willing to activate Lionel Messi's $328 million release clause. That offer was more boast than anything else, but it played up the fact that Barcelona do not have wealthy owners to bankroll their purchases.

The fact is, whoever steps into the Barcelona hot seat will have to confront a changing soccer landscape. The new money is in Paris and London, and the traditional powers in Germany, Manchester and Madrid, have all reloaded. Barcelona, in many ways, have been overachievers. Perhaps the only way they can go is down. Whoever fills Vilanova's shoes should be wary. Even the presence of Messi and Neymar will not guarantee them wins in the Champions League . And while Barcelona are clearly a very good team, it's now open for debate if they remain the world's greatest.