Bayern Munich's squad is the envy of world football. With world-class options at every position both in the starting lineup and on the bench, no team can compete with the Bavarians' quality. And with eight of Pep Guardiola's best XI under 30 years of age, they are set to dominate for years to come.
Yet despite all their class and depth, as of now Bayern have just just three natural center-backs in their team: Dante, Jerome Boateng and Daniel van Buyten.
The former is one of the few first-teamers on the wrong side of 30. And the latter turns 36 in February.
The situation heading into next season is hardly better, with Van Buyten's contract expiring and the Belgian being replaced by Holger Badstuber, who has had back-to-back cruciate ligament surgeries and will not have played professional football for 20 months before the season begins.
Bayern, until recently, had Jan Kirchhoff as an alternative, but last week loaned the 23-year-old to Schalke for the next year-and-a-half.
Beyond the three natural options the only fourth choice who could realistically play in central defense is Javi Martinez, unless Guardiola chooses to redefine Philipp Lahm yet again.
It only takes a brief look to the northwest to realize just how important it is that the Bavarians sign at least one more interior defender. Competitive on three fronts until November, Borussia Dortmund's Bundesliga campaign self-destructed following injuries to Neven Subotic and Mats Hummels.
The club responded by bringing Manuel Friedrich out of retirement and, when he failed, blooded 18-year-old Marian Sarr in a desperate attempt to stop goals from hemorrhaging.
Neither plan worked and BVB lost four of their last six matches leading into the winter break.
Bayern and Guardiola have experiences of their own that should be ample warnings that defense is an area that ought not to be neglected.
Former Bayern coach Louis van Gaal made the mistake of trusting the slow and ineffective Martin Demichelis, Daniel van Buyten and out-of-position Luiz Gustavo. Meanwhile, Guardiola and his successors at Barcelona have repeatedly opted not to sign a center-back to replace the aging Carles Puyol.
The results in both cases were disastrous in the most telling moments. Bayern's defensive weakness was ruthlessly exposed by Inter in the 2010 Champions League final, and a year later the same Nerazzurri that were later crushed by a 7-3 aggregate score at the hands of Schalke eliminated the Bavarians in the Round of 16.
Inter's results against Bayern and Schalke proved that having a defensively weak team opens the floodgates, offering otherwise lesser teams the goals they need to produce stunning and avoidable upsets.
Barcelona, meanwhile, have kept a brilliant record in La Liga, but their defensive performance has become steadily poorer in recent years.
True defenders like Puyol and Eric Abidal have been replaced by less defensively qualified players like natural midfielder Javier Mascherano and forward-minded full-back Jordi Alba.
It's been three years since Barca reached the Champions League final; ever since, a woeful defense has been their undoing.
If Bayern are to make history and win the treble for a second consecutive season, they will be at a sore disadvantage if they do not act to sign cover in the center-back position.
Dante and Boateng are more than reliable enough as starters, but if either becomes injured or is suspended, a strong Champions League team could rip Bayern apart.
Van Buyten's pace and agility aren't even close to sufficient for taking on Europe's best forwards. And the last time Martinez played center-back against an elite striker, Falcao ripped him apart, scoring twice in the 2012 Europa League final.
Curiously, there as yet has been no word from Munich on a possible addition in defense.
Mentioned as options over the summer, rumors of moves for Inigo Martinez and Laurent Koscielny have since dried up as Van Buyten has grown older and Kirchhoff has left the club for a long-term loan.
Most great teams have an Achilles' heel, but few have one so avoidable as Bayern's: A few million Euros' investment would be sufficient to sign a decent stopgap (much like Ricardo Carvalho did at Real Madrid) in the event that Dante and/or Boateng are unable to play in an important match.
A lack of depth at center-back remains Bayern's only weakness and may be the only thing that stands in the way of success in the Champions League.
It would be a shame if such a simple and fixable problem were their undoing in their quest for a double-treble. But at least it makes for less of a foregone conclusion.