As this relentless and uniquely challenging season progresses, beating out demands twice a week it will be back-ups as much as first choices that decide its fate. And on the evidence accumulated so far it will be Manchester City not Manchester United or Liverpool who look best set to capitalise.
Axel Tuanzebe had a superb game against Paris Saint-Germain earlier in this campaign, stubbing out the twin threats of Neymar and Kylian Mbappe with a degree of comfort which suggested he could challenge for the slot alongside Harry Maguire this season.
But the fact he has had just three starts since – one in each of the domestic cups and one league start – suggests Ole Gunnar Solskjaer sees flaws in his game that leave him vulnerable at the top level.
Given a first Premier League start against Sheffield United last night Tuanzebe did not advance his claims, having a hand in both goals.
On the first he failed to get a head above the much shorter Kean Bryan and for Sheffield United’s winner failed to clear his lines when he had the chance then deflected the ball past his keeper.
Tuanzebe is probably comparable to Rhys Williams at Liverpool, another promising young player enduring a baptism of fire in a season stretching resources everywhere.
But he is not remotely close to the reliability of back-up provided by Nathan Ake or Aymeric Laporte at cross-town neighbours City.
It is down to the player himself to prove doubters wrong and he may well do if he can relocate the player who impressed so much against PSG.
But for now Solskjaer’s back up options look likely to weaken not strengthen his hand in the hunt for the Premier League title.