Where might Barcelona seek the weak link within a Bayern Munich side chasing a ninth successive victory, in a team who have 32 goals from their last eight outings?
Should they put pressure on the rookie, perhaps, as Real Madrid attempted at this stage of the Champions League last year?
For David Alaba, the memories of 12 months ago, and his first European Cup semi-final, are especially vivid. But the youngest, 20, of the likely starters in tonight's collision in Germany can look back on them as a rite of passage in the maturing of one of Europe's outstanding attacking full-backs.
In the Madrid leg of the tight contest for a place in the 2012 final, Alaba would be fiercely targeted by Jose Mourinho, the Madrid coach. Mourinho's instructions to his best long passer, Xabi Alonso, were to pepper the teenager with drilled and floated passes, examine his positional instincts, test his abilities in the duel.
Angel Di Maria, wide on the right of Madrid's midfield, had been told to put fear into Alaba, to tease. It appeared to be working when Di Maria slipped past him in the first of their jousts. Fate then seemed to be bullying him, too: Alaba gave away a penalty with an unfortunate handball. He picked up a yellow card.
That was after six minutes. By the end of a night which see-sawed one way and the other, the booking would look more personally costly. It meant Alaba's suspension from a final he had been crucial in enabling Bayern to reach.
In the course of the two hours against Madrid, the full-back grew from novice to totem. By the time of the shoot-out it seemed entirely natural the poised teenager should take Bayern's first spot-kick. He converted it.
Bayern would miss Alaba in the final, where his zest down his particular flank, his telepathy with Franck Ribery, the winger, and his coolness from the penalty spot just might have made a difference to a showdown won by Chelsea via a shoot-out.
"For me, David Alaba is one of the biggest talents in European football," said Karl-Heinz Rummenigge, the Bayern chief executive and former West Germany captain. Philipp Lahm, the captain and right-back, praises Alaba's "outstanding talent and amazing ability to read the game".
Alaba has plenty of admiration in his native Austria, too. His country's Footballer of the Year for the past two years, he is often given a role in central midfield for the national team so that their game plan can revolve around him.
He was their youngest debutant, at 17, and it was in Austria's interests to seal his future because his background made him eligible for other countries: the Nigeria from which his father moved to Vienna to study in the 1980s, before making a living as a musician and a DJ; or the Philippines, where his mother, a nurse, was born.
Alaba's diverse background has made him something of a role model for a younger generation of Austrians, mindful their nation has experienced a rise by a political far-right in the 21st century.
Bayern recruited Alaba, at 17, from Austria Vienna, and Rummenigge proudly counts him as a shining example of the best of the club's scouting and youth-development programme, alongside Bastian Schweinsteiger and Thomas Muller.
But Bayern still envy the sort of home-grown excellence Barcelona consistently draw upon, which is in part why they have contracted Pep Guardiola, the former Barca coach, from next season.
Sometimes even the fabled Barca academy has shortsighted moments. One concerned the teenaged Jordi Alba. Born in the capital of Catalonia, he was allowed to leave Barca's youth ranks at 16.
While they liked his speed, his tenacity and his strong left foot, he was considered a little too short for the left-back position, for defending the far post.
Barca were wrong. His performances in his early 20s for Valencia made Alba Spain's first-choice left-back ahead of last summer's European championship.
By then, he had become the last signing Barcelona made in the Guardiola era. He has given Barca greater zip from left-back, and a healthy dose of aggression.
Alba, at 24, is still diminutive, but as Lahm would testify, standing only 5ft 6ins need not be a handicap for his position.
The key to mastering the demanding job of modern full-back makes mobility a more important asset than height or might.
Tonight, two of the game's little giants of the job, Lahm and Barca's Dani Alves, will expect to show that. In direct opposition to them, again and again, down the flanks, will be a pair of left-backs with rising reputations, and chiming surnames to keep commentators alert: Alba and Alaba.