So, while there were surprises in Paris, there were certain fears that were realised too.

Such a chastening defeat has been a long time coming. Here's why. ...

The blueprint

Few coaches are as studious as Unai Emery, and Luis Enrique pointed out before the match that the PSG manager had the added benefit of having faced Barca so many times -- even if his first win in 23 games before Tuesday only arrived last season with Sevilla.

But it's unlikely Emery's previous encounters with Barca would have provided him with the majority of his inspiration. He needn't have gone back so far. A case study of the Blaugrana's performances over the last few months would have been sufficient.

Dropped points against Alaves and Malaga at the Camp Nou are perhaps Barca's most shocking results this season, but it's their performances in draws against Real Sociedad, Villarreal and Real Betis where their weaknesses have been most obvious. All three of those teams pinned Barca back with high pressing, and Luis Enrique's side were clueless as to how to counter it.

In each of those games, they were saved by a Messi goal or assist. But if each of those teams had a little bit of extra quality and luck in the final third, they may have been out of sight before Messi popped up.

The same could be said for Atletico Madrid, who rightfully feel they would have knocked Barca out of the Copa del Rey last week with better finishing and more fortune.

PSG didn't need any luck, because they had the quality.

Inconsistent for almost a year

Going further back, Barcelona have been alarmingly inconsistent since last March, when a 39-game winning run was ended by Real Madrid. That was followed by two more losses in La Liga, and what was a 10-point gap over Madrid with eight games to play ended up being just a one-point lead going into the final day of the season. Luckily for him, Luis Enrique's side got over the line.

They also won the Copa del Rey -- just beating Emery's Sevilla in extra time -- to add a Double to the previous season's Treble, but they were deservedly dumped out of the Champions League by Atletico.

That inconsistent form has continued into this season. They've dropped points eight times in the league, been tested in the Copa by Athletic Bilbao and Atletico, and were well beaten on trips to Manchester City and PSG.

Weakness in midfield

It's no surprise Barca's results have become so inconsistent when there's a lack of consistency and control in midfield -- an area they were once famous for. It is a given that Sergio Busquets and Andres Iniesta start, but recent injuries meant they were probably not at full fitness at the Parc des Princes.

Who plays alongside them has often been a lottery, but Enrique tends to lean towards Andre Gomes. Despite his potential, the Portuguese international has struggled to adapt, and his continued selection has been questioned. In Paris he was particularly poor, missing Barca's best chance, picking up a booking, not shutting down runners and not helping out right-back Sergi Roberto.

Ivan Rakitic has not been in great form this season, but it's surprising how far his star seems to have fallen. Without that control in midfield, Barca are reliant on Messi, Neymar and Suarez to resolve games for them.

"Barca are not what they were ... footballistically speaking," Lluis Mascaro wrote, even before the PSG horror show, in regards to a shift away from the philosophy instilled by Johan Cruyff.

La Liga giants Barcelona were thoroughly outplayed, leaving their Champions League hopes in tatters.

The Luis Enrique doubt

There will be few doubting this is Enrique's last season in charge. Already evasive about the chances of renewing his contract beyond its summer expiry, Barca's almost certain elimination from the Champions League is likely to accelerate his exit.

After Tuesday's game, Enrique clashed with a journalist, and given his relationship with the local media throughout his tenure at the club -- during the good times and the bad -- he may be set for a difficult few months.

"Barca played without a coach in Paris," said Diario Sport editor Ernest Folch after the PSG game, wasting no time sticking the knife in.

It's a comment that will be echoed throughout the Catalan media in the coming days, weeks and months, and it will only get worse if, alongside their likely departure from Europe, Barca don't make inroads on Real Madrid at the top of La Liga.

On top of that, Busquets has said that PSG were tactically superior to Barcelona and better prepared.

Is that a dig at his coach? Perhaps. COPE say the players are already prepared for him to leave in the summer -- a feeling that predates being humiliated in Paris.

Luis Enrique's future has been plunged into further doubt after a chastening night in Paris.

Right-back failings

You always get a chance against Barcelona.

One particular weakness has been at right-back. Sergi Roberto has impressed, having converted from midfield to become Dani Alves' replacement. But he has always come up short in the big matches. Against PSG, you almost felt sorry for him. Gomes simply didn't provide him with the protection that Rakitic used to supply Alves.

The blame for that has to fall on the club. Aleix Vidal's season-ending injury at the weekend was a setback, but he hadn't provided many solutions until recently. The failure to sign a right-back -- last summer or in January -- was an error.

Elsewhere, Jordi Alba had an off night, while Gerard Pique and Samuel Umtiti -- a world-class defender and a young player with huge potential -- made mistakes, although they weren't helped when they were on the ball by a lack of options from the midfielders.