It was ten years ago Sir Alex Ferguson dubbed them the best team he had ever faced but those left from Barcelona's iconic generation still have work to do, reports AFP.
Three remain and when Lionel Messi, Sergio Busquets and Gerard Pique line up against Liverpool on Wednesday, they may wonder if this could be their best chance of another, and perhaps final, Champions League triumph.
Xavi and Iniesta have gone, succeeded by the all-encompassing Ivan Rakitic and, more recently, Arthur Melo, who could mature into the kind of player his predecessors would admire.
Messi, who turns 32 in June, Busquets, who will be 31 in July, and Pique, already 32, have hung on, driving the club through fresh cycles of success.
But in some ways perhaps, Ferguson was right. They could never sustain the Guardiola method in full, in part because pressing began to neutralise possession but mainly because that group of players was unique.
In the Champions League, glory came again quickly in 2011, United again the victims, but from 2012 to 2018, it followed only once more, after beating Juventus in 2015.
Messi, Busquets and Pique have played in 34 Champions League semi-finals matches between them and while the likelihood is there will be more to come, nothing is guaranteed. If the next takes as long to arrive as this one, Messi will be almost 36.
When Ernesto Valverde took charge at the start of last season, Barcelona were wounded by consecutive Super Cup defeats to Real Madrid.
"For the first time I feel inferior to them," said Pique.
Now they sit 18 points ahead of them in the league, having finished 17 clear of them last season. But inferiority in Europe still rankles. It is Madrid's name on the cup next to four of the last five years.
And for the remnants of one of Barcelona's most symbolic eras, time is running out to put it right.
There are green shoots emerging, a new cycle - Arthur, Ousmane Dembele, Clement Lenglet and Carles Alena - coming through.
Frenkie de Jong could face Barcelona in the final in Madrid, in what would be his last Ajax appearance before joining the Catalans in July. He may not replace Busquets but the 21-year-old will, at the very least, challenge him.
Pique has been one of his team's standout players in central defence but there are plans there too. The 19-year-old Jean-Clair Todibo arrived from Toulouse in
January and Matthijs de Ligt could follow De Jong from Ajax in the summer.