Having set a new Spanish record with a 39-game unbeaten run, they have come tumbling back down to earth after Real Madrid beat them at the Nou Camp last month. They have now lost three of their last four games and crashed out of the Champions League in the process.
And no one's form has dropped more drastically than Lionel Messi's. The Argentinian, so often the inspiration behind Barcelona's genius, has now failed to score or assist a goal in any of his last five games – the worst drought of his career.
Messi was noticeably out of sorts as Atletico Madrid secured a famous 2-0 win over the reigning European champions at the Vicente Calderon on Wednesday night.
Not only did he fail to register a shot on target, but he covered less ground than every Barcelona player other than goalkeeper Marc-Andre Ter Stegen.
So what is going on with the five-time Ballon d'Or winner? Is he finally falling into decline? Has he fallen out with Luis Enrique? No, according to Spanish radio Cadena COPE , Messi is secretly suffering from a serious muscle injury.
Usually a reliable source of news, the radio station's 'El Partido de las Doce' show claimed Messi is having to take regular trips to Sacile, Italy to see specialist Dr Giuliano Poser for a "kinesiological" treatment.
This has, allegedly, been going on for several weeks, which is just about the same time that Barcelona's season started to unravel. While the treatment is going well, the problem is still very much there and Messi is expected to undergo more of these sessions before he is fully recovered.
There is nothing new about a key player refusing the rest during an important part of the season. Playing through the pain barrier is something most footballers will do during their career, but is it the real reason for Messi's poor form.
It seems fanciful that Messi could travel to Italy on a regular basis without being seen once or twice. As the best footballer in the world, his face is one that the majority of people in the world would instantly recognise.
Cadena COPE is famously pro-Barcelona so perhaps they are attempting to provide an excuse for their struggling star. Or perhaps Barcelona's media wing is attempting some recon work in such a difficult time.
Barcelona have a chance to get their season back on track this weekend when they welcome Valencia to Camp Nou. Last time they were there, Barcelona won 7-0. My, how they could do with a result like that now.