When it comes to assessing Sunderland’s promotion potential, the biggest question mark hangs over the strength of their squad.

With the season a third of the way through and with the Black Cats sitting top of the table - albeit only on goal difference - they have demonstrated that their first XI, and those immediately adjacent to the first XI, can compete with anyone in the Championship.

But to sustain a promotion challenge over the course of a gruelling 46-game season it is not enough merely to have 14 or so players who you can hang your hat on.

It takes more than that.

And the depth of Sunderland’s squad is about to be tested - really tested - for the first time when their season resumes at Millwall following the international break.

Because last Saturday’s second half against Coventry City was not only costly because Sunderland dropped two points after letting slip a two-goal lead, but also in terms of personnel.

Romaine Mundle and Alan Browne both limped off against the Sky Blues and must be considered injury doubts at the very least, while Trai Hume collected his fifth yellow card of the season and must now serve a one-match suspension.

Patrick Roberts will also be absent at The Den after he was booked for the fifth time this season in the first half.

And Jobe Bellingham was already ruled out as he completes a three-game ban.

Unless Mundle and/or Browne are passed fit, that adds up to half of Regis Le Bris’ first-choice outfielders unavailable.

Le Bris will need to come up with solutions to his selection problems and it is likely that the team will have an unfamiliar look next weekend, either in shape or with square pegs in round holes - or both.

There is no obvious replacement for Hume at right-back, for instance. He could ask Luke O’Nien to fill in, but that would mean breaking up his central defensive partnership with Chris Mepham.

If Mundle does not make it, will he play Wilson Isidor on the left? Or does playing your main goal threat out wide come at too greater cost?

Could Eliezer Mayenda or Nazary Rusyn offer answers? Will Le Bris bring the likes of Adil Aouchiche or Abdoullah Ba in from the cold?

Or will he shift to 4-4-2 or even three centre-backs?

Le Bris will have been weighing up all options and permutations over the international break.

To be without possibly half your first-choice team is rare but it does happen.

What Le Bris decides to do, and how well it works, will tell us much about the strength in depth of this squad and how much work will be needed in the January transfer window to keep Sunderland’s promotion push on track.

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Life comes at you quickly in the Championship.

One minute you’re sitting pretty, five points clear at the top of the table; a week and three - unbeaten - games later that lead has been whittled down to just a couple of goals in the goal difference column.

Three successive draws, at QPR and Preston, and then at home against Coventry, saw Sunderland extend their unbeaten run to eight games but Sheffield United are on the charge after four wins in a row and now loom large in the rearview mirror.

I wrote last week about the QPR and Preston games, but last weekend’s 2-2 against Coventry was even more frustrating.

It had all started so well with two goal-of-the-season contenders from Wilson Isidor and Dennis Cirkin in a good opening 45 minutes, so Coventry’s second half comeback was a kick in the teeth.

In the immediate aftermath the sense of disappointment at the Stadium of Light was palpable and time has done little to dispel the sense of a major opportunity missed.

Zoom out to see the bigger picture, however, and things look much better.

Top of the table going into the November international break while averaging better than two-points-per-game is pretty good going and, I would suggest, still sees Sunderland running well ahead of the pre-season expectations of all but the greatest optimists.