Barcelona enjoyed a sensational second half of the campaign to take a clean sweep of trophies last season, but the task of staying on top promises to be even tougher. After a difficult start to Luis Enrique’s reign, the integration of Luis Suarez to form one of the most devastating forward trios ever seen helped fire the Catalans to the Primera Division title, along with Champions League and Copa del Rey prizes.

But there are already signs that it could be another slow start to this season. Certainly preseason has been far from ideal. After a grueling tour of both coasts of the United States, Barcelona faced a long trip to Georgia capital Tbilisi for the UEFA Super Cup. Although they triumphed 5-4 in a thrilling extra-time encounter with Sevilla, the full effects of their exertions were evident when being humbled 4-0 at Athletic Bilbao in the first leg of the Spanish Super Cup. The performance was not much better in a 1-1 draw in the return leg, meaning Barcelona have already lost the chance to claim all six available trophies in 2015. And they are unlikely to be at full force when their Liga title defense kicks off, against Athletic, on Sunday.

But it is the whole of the first half of the season which could be a real test of Barcelona’s physical endurance and resilience, as well as Luis Enrique’s ability to manage a squad that is short on depth. Barcelona remain under a transfer ban, meaning that even though they’ve signed former Atletico Madrid schemer Arda Turan and Sevilla’s versatile right-sided player Aleix Vidal, neither will be able to play before January.

By that time Barcelona will already have had to travel to six of the top seven clubs in La Liga last season -- Athletic, Atletico Madrid, Sevilla, Real Madrid and Valencia. They will have also begun their attempts to become the first team to win back-to-back Champions Leagues as well as attempting to claim the Club World Cup in Japan.

In the Spanish Super Cup, there were already indications that Barcelona’s fringe players could struggle to maintain the team’s momentum if the star names are rested. A big onus has been put on Barcelona’s young prospects to step up, not only because of their punishing schedule and the club’s ban on adding new players, but also because the club has allowed some more established players to depart.

While the exit of legend Xavi was long expected and understandable, the decision to sell Pedro to Chelsea this week is more curious. The World Cup winner may have found himself behind Messi, Neymar and Suarez last season and keen for regular first-team action, but surely Barcelona could have held on until January. With the club also cashing in on young attackers Gerard Deulofeu and Adama Traore, they can ill afford to be without their famed front three for any length of time. It is a risky game Barcelona are playing.

There is an early concern at the back, too. The man who played such a big part in giving Barcelona the best defensive record in La Liga last season, Gerard Pique, will be suspended for the first four games of this season after his sending off for using abusive language toward an assistant referee in the second leg against Athletic Bilbao.

There are, for sure, challenges aplenty. Yet if they can keep everyone fit and suspension free then they remain surely the most talented team in Spain and the world. There is little reason to think that Messi, Neymar -- once he fully recovers from mumps -- and Suarez won’t repeat their incredible performances of last season given that they have now had a year to build even stronger chemistry. Behind them, Ivan Rakitic has had a full season at the club and, having becoming increasingly influential following his transfer from Sevilla last summer, should take on even more responsibility in midfield.

And, besides, Barcelona already know that they can come through to lift the title after a poor first half of the campaign. Last season the Blaugrana trailed Real Madrid by four points in January, but lost just one of their last 21 games to pip Real Madrid to the championship by two points.

Betting odds (via Oddschecker): Barcelona are 4/6 favorites to lift the title, ahead of Real Madrid at 13/8 and Atletico Madrid at 16/1.

Prediction: There will be some difficulties along the way, but Barcelona still have incredible quality in every area of the pitch. With main rivals Real Madrid facing their own problems adapting to life under new manager Rafa Benitez, the Catalans are rightly favorites to retain their crown.