It is hardly the least intriguing of the many questions that await an answer at the Etihad this afternoon. Will the real Wayne Rooney stand up in his favourite position, just behind Robin van Persie, and provide the link between two potentially world-class players that wins the day for his team? "The two of them maybe aren't gelling as well as everybody would have liked," Sir Bobby Charlton said yesterday.
Having missed half-a-dozen games early on in the season with a badly gashed knee, Rooney has given the impression of easing himself back in, until now. He then had to sit out a further two matches with tonsillitis, against Norwich and Galatasaray, in both of which United were beaten without scoring.
Two goals at Reading last weekend were only his fourth and fifth of the campaign in 15 appearances, and it was significant that when Sir Alex Ferguson made 10 changes from that game for the dead Champions' League rubber against Cluj in midweek, Rooney was the only player to be retained. "Wayne has got another 90 minutes behind him, he is close to full fitness and hopefully he will be approaching top form come Sunday," Ferguson said afterwards. The manager has made regular references to his fitness and even his "shape", implying that, rather like a latter-day Paul Gascoigne, he needs to be in the very best condition to perform, and even that after being out for any period he takes three games to hit his stride again.
Reading was the third, and probably his best performance of the season, though the oddity on Wednesday was not so much his inclusion as his position, stuck out on the right of midfield. It did not work, any more than a role out on the left tends to, and it is no surprise to learn that the player himself prefers to be involved more centrally.
After the Cluj game, Rooney made a joke of his supposed versatility, saying: "I think I've played in every position on the pitch this season!" He added tactfully: "I'm enjoying it, it is a different experience and a different step for me."
In the past he has spoken of a preference to play just behind another striker. Talking to the Performance Four Four Two website, he said of being cast as the main striker: "It's hard when you're 5ft 10in and you're up against centre-halves who are 6ft 3in, but it's my second favourite position after playing off another striker. Out wide would be third choice." A distant third, probably, although those who play for Sir Alex are best advised to keep their counsel about precisely what they like and don't care for.
The dynamics at United changed with the arrival of Van Persie who, though not a classical No 9, works happily as the furthest man forward, as long as he has some support. Ideally that comes from a Rooney-like figure who can both supply him from a deeper position but also interchange and accept scoring opportunities with the flair of a man who recorded 35 goals last season and 34 two years earlier.
When Rooney is the main man, for either United or England, he can become frustrated if he is not seeing enough of the ball and fall into the trap of chasing too far back to look for it. His capacity for work can never be faulted, and in his various midfield roles he takes responsibility almost too far at times and can even be found as the last defender, which is neither his job nor his strength.
He does, however, clearly think more about the game than detractors might give him credit for, and at 27, in his ninth season with United, he has clear ideas about the best way for the team to play: "I think our strength is getting wingers on the pitch, getting the ball out wide and attacking and crossing into the box. That's obviously the way United have played for years so it is one of our strengths." The clear implication is that he would rather be one of those on the end of the crosses than supplying them.
A tighter midfield diamond, tried briefly this season, was quickly dropped but injuries to Antonio Valencia and Nani have left Ashley Young as the only natural wide player (a role that no longer suits Ryan Giggs). It has become the case that Rooney, Danny Welbeck or Nick Powell tend to be used there.
Accepting the limitations imposed by those injuries, what United supporters will hope to see this afternoon is, nevertheless, a bolder approach than the one in the corresponding game last April, when only a draw was required to keep the League leadership and promise the title. Rooney played on his own through the middle and his team failed to have a significant shot on target.
He says of today's task: "We want to do better there than last year. We are in a good position in the League and don't want to give that up this early. We have started reasonably well and are in a great position. With City out the Champions' League, they are having a bit of a tough time and I think everyone can see that behind the scenes. If we win, it will put more pressure on them." And the role he expects to play? "Who knows. I'll see where I am on Sunday."
Manchester City (4-2-3-1): Hart; Zabaleta, Kompany, Nastasic, Clichy; Y Touré, Barry; Silva, Tevez, Aguero; Dzeko.
Manchester United (4-2-3-1): De Gea; Rafael, Ferdinand, Evans, Evra; Carrick, Fletcher; Welbeck, Rooney, Young; Van Persie.
Manchester City v Manchester United is on Sky Sports 1 today, kick-off 1.30pm