First there is the injury crisis that saw makeshift defender Javi Garcia struggle at centre-half.
While you cannot account for injuries sometimes, City are far too reliant on Vincent Kompany, who does pick up the odd injury and has done throughout his career.
Matija Nastasic is a fine defender but is still young and developing, leaving Joleon Lescott as the only other specialist senior centre-half at the club. Micah Richards is barely even a right-back these days, having seen his career derailed by fitness problems.
Even without injuries to Kompany and Nastasic, that is not acceptable for title-challengers, who need at least two players in each position.
The issue here is that City have not added to their backline this summer. Defending was a bit of problem for Roberto Mancini as, while City had the best overall goals-conceded tally in the Premier League last season, there was a tendency to collapse under pressure.
In the league, City conceded 34 goals – which, while the lowest in the division, is not exactly at the level of Jose Mourinho’s old Chelsea sides, who would let in a meagre 15-20 in some campaigns.
Dig beneath the surface and you a faint pattern emerges. Granted, there were 14 clean sheets, but the six matches City lost were by the following scorelines: 3-2, 3-2, 2-0, 3-1, 1-0, 3-1. They lost by the odd goal in three on four occasions.
Champions United, meanwhile, lost one match 3-2, one 2-1 and the other three 1-0. When City fall apart, they often do so spectacularly. A vague pattern, but a pattern nonetheless.
The fine margins are what differentiate between champions and runners-up. Those margins are stretched and further exposed in Europe, where City were again poor.
This points to a soft centre, no more so than when Kompany is absent. But City have another problem, which is the questionably long-term form of Joe Hart.
Hart seems to be resting on his laurels. The England keeper looked like he was among the best in the world a few years ago, but he appears to have regressed.
A tacky shampoo ad and some high-profile blunders could see him going the way of Iker Casillas, well ahead of schedule – except that, unlike at Real, there is no genuine competition to Hart at Eastlands. It's not even worth going there with England...
Costel Pantilimon is an able deputy but nothing more. He certainly does not put enough pressure on Hart, who is bordering on the complacent.
Hart’s shot-stopping is still excellent, and he remains a dominant and vocal force in the box. But his decision making and concentration appear to have slipped, as displayed with his wild flap for Fraizer Campbell’s first goal and Cardiff’s second.
Hart is still a brilliant keeper, but he suffers a malaise because he is not being kept on his toes by a top keeper breathing down his dandruff-free neck.
City are expected to sign a new, experienced defender, with Atletico Madrid’s Martin Demichelis reportedly close to reuniting with his former Malaga boss only weeks after joining Los Rojiblancos.
But if Pellegrini is to really mark himself as a ‘holistic’ coach, he should be looking at a proper deputy who can compete with the fading Hart.
Stoke City signed Jack Butland with a view to replace Asmir Begovic, and they would be open to an offer for the Bosnian – with City hardly short of a few bob, it would be a £10million well spent.
Things are never that easy at Eastlands though, with the club’s hierarchy keen to focus on big-name attacking players as they stick to the football oligarch blueprint.
It is believed that Demichelis is yet to join for this reason, with the board reluctant to pay £4m to buy out a 32-year-old defender’s contract.
Yet they spent over £100m on Alvaro Negredo, Jesus Navas, Fernandinho and Stevan Jovetic - all in positions where they were more than well-equipped last season.
Would City's owners countenance spending on a keeper when they already have England’s Number One? Possibly not. But, with the Premier League more competitive than ever at the front end, it could be the difference between first and – heaven forbid – fifth.