Who can solve Gareth Southgate's centre-back problems for England?
English football seems to go in cycles. Remember back during England's so-called Golden Generation, when the accepted wisdom was all the team was missing was a left-sided midfielder?
Now the tables have turned, and after a hugely disappointing defeat against the Czech Republic, questions are being raised about England's defensive partnership of Michael Keane and Harry Maguire.
For 15 years or so, the English defence was presided over by Sol Campbell, Rio Ferdinand, John Terry and Gary Cahill – but nobody has really picked up the mantle since these players left the frame.
Now it feels like at least one, if not both, of those slots are up for grabs. Here's who'll feel they might have a shot at being in the shake-up for Euro 2020...
Were it not for a cruciate ligament injury last season, Holding may have already been called up to Gareth Southgate's squad. The Arsenal defender started last season very well, and many fans are hoping his return to fitness will help plug the Gunners' leaky defence.
Comfortable on the ball and consistent when given a run in the team, Holding plays like an old head on young shoulders, and those qualities could make up for the lack of an established senior pro at the back.
Wolves fans might be feeling confused about why Coady hasn't already got a call-up. He was an integral member of their back three as well as their captain, and extremely impressive in helping Wolves achieve European qualification last season.
Coady is also a good passer and used to playing a high-energy, counter-attacking game, but Southgate has previously indicated that he's unsure how Coady would fare in a back four. Calling him up might be a gamble, but it's possibly one worth taking – especially if England's manager reverts to his back three soon, as also suggested.
Dunk has earned a cap already under Southgate, but found himself out of the squad this time around.
However, the stopper may have cause to feel unlucky. The Brighton defender leads Michael Keane in passes made, pass completion, tackles and interceptions this season. He also put in an excellent performance for the Seagulls in their 3-0 victory over Spurs, showing how important he is to Graham Potter's side.
Tomori joined fellow Chelsea youth prospects Mason Mount and Tammy Abraham in getting called up to the England squad after an impressive start to his season, but had to make do with a place on the bench.
An excellent goal against Wolves caught the eye, but his overall play has been impressive: he's in the top 10 for interceptions and tackles made among his peers this season.
Tomori's pace also gives him an edge over some of the other candidates, and it's thought that he may get a chance to prove his worth in Monday's game against Bulgaria.
A wildcard maybe, but given the rush to praise Sheffield United's overlapping centre-backs under Chris Wilder, maybe it's worth Southgate having a look at one of them.
O'Connell hasn't represented England beyond under-18 level, but has started the season well and particularly impressed in Sheffield United's narrow defeat to Liverpool.
He's another who plays in a back three, and isn't afraid to get forward and pass the ball. However, the 25-year-old also leads his defensive competition in clearances and blocks this season, showing he's not afraid of doing the dirty work either.