It was a bit of a mixed night for Roy Keane on Champions League duty in the ITV studio at the Emirates on Tuesday. On the one hand, taking issue with Mikel Arteta's assertion that Arsenal had done enough to deserve at least a point against Borussia Dortmund, if not all three, the former Manchester United captain came out with the immortal line: "At this level the game's all about putting the ball in the net". Since competitive football at any level is about putting the ball in the net, and in this respect the Champions League is no different from a League Two play-off or an FA Cup qualifying round, Keane will not be picking up any bonuses for profundity.

On the other hand he did manage to scratch an eight-year itch and make the 10 o'clock news with his incisively caustic remarks about Sir Alex Ferguson. Loyalty cuts both ways, was the gist of his comments, and the newly retired United manager ought to show a bit more gratitude to the players who helped bring him success.

Keane looked quite pleased with himself saying this, as if he had had it in mind for quite a while, and the merest hint of playfulness – well, about 5% of the entire facial expression – strayed briefly across his unyielding features. The real killer quote, however, was a simple: "I just don't think the manager needs to do it."

That should be ex-manager, of course, but let that pass. Keane obviously has some vestigial respect for Ferguson, and why should he not, if loyalty does cut both ways? But why would a manager who retired in a blaze of glory, universally admired and saluted even by rivals from the City and Liverpool camps, want to produce a coda to his unparalleled contribution to the game by having a go at Stewart Downing and debating whether David Beckham counts as a United legend? There is no way Ferguson can tarnish his legacy, the achievement is too solid, the case for greatness unarguable, but in inviting reasonable criticism from Keane and possibly others he has already surrendered a little of the high ground.

Ferguson's great trick as an active manager was to convince the world, and especially the bit of it that came into contact with Manchester United, that he was right all the time. Even in the face of obvious mistakes such as Massimo Taibi, Bébé, Eric Djemba-Djemba and the Rock of Gibraltar dispute, his reputation for wisdom and sound judgment survived intact. That was largely because, while in situ, it could automatically be argued that everything he did was ultimately for the good of the club.

There was no need to look for a hidden agenda, he was simply doing his job, and doing it very well. Suffice to say at this point that retirement subtly alters that dynamic, especially when it is permanent retirement and not, say, Kenny Dalglish between jobs or Harry Redknapp still touting his suitability for the England position. Keane's observation, essentially a question, remains a pertinent one.

Returning to what Keane should have been talking about, the manner of Arsenal's defeat proved, as if anyone needed telling, that the Champions League is a big step up from Saturday afternoons in the domestic comp, and that Norwich's only similarity to Dortmund is the colour of their shirts.

At the start of the week it looked as though Arsenal had finally cracked it and they might be able to pass their way to success after all. Mesut Özil described Jack Wilshere's goal against Norwich as like playing on PlayStation, and any number of people announced they had seen the goal of the season already. Yet Arsenal were back to passing without an end product against Dortmund. Their only goal came from a cross – of all things – that most Premier League goalkeepers would have dealt with, and though the Germans appeared to be playing a possession game of their own at the start of the second half it turned out they were merely inviting Arsenal to advance in order to demonstrate their devastating ability to strike on the counter.

It is perhaps fortunate that Arsène Wenger's players have the chance to regroup at Crystal Palace this Saturday, for the half-dozen games that follow could play a big part in shaping Arsenal's season. First up there are home games against Chelsea and Liverpool, then trips to Dortmund and Manchester United followed by Southampton and Marseille at home. None of those are straightforward and, assuming the Gunners can keep their Champions League hopes intact until the last group game, they could hardly have been handed a more daunting venue than Napoli away on 11 December.

Lee Dixon, being the confident, glass half-full antidote to Keane's stern pessimism, suggested Arsenal might be capable of going to the Westfalenstadion and the Stadio San Paolo and gaining a result. So they might, but it is not a qualification route anyone would have chosen, and if Arsenal can survive they will thoroughly deserve a place in the knockout stage.

At the moment Group F is the most fascinating and unpredictable of the Champions League tables, with Wenger, Jürgen Klopp and Rafa Benítez all on six points after three games. They could all take points off each other, and probably will, and Marseille could yet have a say. One good team must go out. Arsenal have two unenviable away trips but one more home game that appears winnable: the entertainment should be first rate. You can be sure there will be twists and turns yet, as Ferguson used to say. Back when he was a manager.