Manager Xavi has brought about a huge transformation at the Blaugrana, and Sunday's thrashing of fierce rivals Madrid had the football world talking. None more so than Muller, who tweeted about the Blaugrana to laud their huge win in the El Clasico.
Muller tweeted (via Mundo Deportivo):
"Congratulations FC Barcelona. It was a pleasure to see this crazy exhibition tonight. Chapeau."
The 32-year-old, interestingly, played a role in Barcelona's fall from grace. A Man-of-the-Match performance saw his Bayern Munich side destroy the Blaugrana 8-2 in the UEFA Champions League quarter-final two years ago.
Since then, the Blaugrana's fortunes have nosedived and their misery was compounded by the departure of the legendary Lionel Messi last summer. However, fast forward seven months, Xavi has taken them third in the La Liga table and even pushing for an unlikely title challenge. Barcelona now trail leaders Real Madrid by 12 points but have a game in hand.
Barcelona to be a force to be reckoned with next season
When Xavi's side exited the UEFA Champions League in the group stage this season, many fans feared the worst.
This was a team not used to playing in the second tier of European football. However, they are now fighting for the UEFA Europa League title, having reached the quarter-finals.
Since their Champions League exit, which was hastened by Muller's Bayern Munich beating the Blaugrana 3-0, Xavi's men have turned things around spectacularly. There is a real sense that they could be on the precipice of challenging on all fronts next season.
The Blaugrana have been linked with a number of talents, including Borussia Dortmund hitman Erling Haaland, AC Milan midfielder Franck Kessie and Ajax's Noussair Mazraoui.
The club have also been touted with moves for Chelsea defensive trio Antonio Rudiger, Andreas Christensen and Cesar Azpilicueta, who are out of contract this summer.
Having already made some inspiring changes at the club midseason, with an pre-season under their belt, Xavi's side could be the total package come next season.
Players will have even more experience learning 'Xavi Ball'. More addition to their already impressive squad could see them challenging with the European bigwigs again.
Sunday's win over Los Blancos should give them the Blaugrana confidence to go on and achieve greatness under Xavi. They are unbeaten in their last 12 games, with the likes of Pierre-Emerick Aubameyang, Ousmane Dembele and Pedri in red-hot form.