De Gea found the aerial demands of English football taxing to begin with and will doubtless hope his fellow Spanish speaker encounters the same problems.
At 6ft, Bravo is not the tallest goalkeeper and the prospect of the 6ft 5in Zlatan Ibrahimovic, 6ft 4in Marouane Fellaini and 6ft 3in Paul Pogba towering in the air would be daunting for any newcomer, regardless of their age.
Guardiola looked up, almost ominously, when - unprompted - he raised the subject of United's physical supremacy, an admission that ran counter to his relaxed approach about Bravo.
"The set-pieces with these tall guys ...," he said. "They are taller than us, it's impossible to control that".
All power to the full-backs
It was almost cathartic for United supporters to see their full-backs being given licence to go forward again after Mourinho lifted the straitjacket imposed by his predecessor, Louis van Gaal.
Indeed, the success of Luke Shaw and Antonio Valencia or Timothy Fosu-Mensah, who could start over the travel-weary Ecuadorian, have overloading with the wide players on the flanks may have a significant bearing on the outcome of the game given their importance on the counter-attack.
By the same token, Guardiola will place a premium - defensively and offensively - on his own full-backs, albeit in a different way.
The City manager does not appear to have the same confidence in his full-backs as Mourinho, which may explain why he is reported to have blocked new contract negotiations for Gaël Clichy, Bacary Sagna and Pablo Zabaleta, but their multi-purpose roles have been one of the most striking facets of the way the Catalan wants his side to play.
Against United, it is unlikely to be much different when City have the ball - Clichy and co will push up into midfield, helping to form an M shape with Fernandinho and the two centre-halves which, among other things, allows the wingers to occupy the opposing full-backs - but when United are attacking they will be expected to press the wide players as quickly and intensely as possible.
The kids are all right
There will be nine players from both sides aged 23 or under who can expect to play a prominent part.
Central defenders Eric Bailly and John Stones, both 22, have enjoyed promising starts to their respective United and City careers, even if this will represent comfortably their toughest tests yet.
Raheem Sterling, named Premier League player of the month for August on Friday and reinvigorated under Guardiola, has shone in a way his United counterpart Anthony Martial - his team's best outfield player last season - has yet to this term.
But, above all, the eye is likely to be drawn to Kelechi Iheanacho and Marcus Rashford, two teenage sensations in a hurry to make a name for themselves.
Iheanacho is the obvious candidate to fill the void left by the suspended Sergio Agüero - unless Guardiola goes down the route of using a false nine - and it is some void.
The Argentina striker has scored eight of City's 25 derby goals since he joined the club in 2011, including their last three in this fixture, but Iheanacho, like Rashford, is not a youngster who seems fazed by the big occasion.
The Nigerian's 14 goals have come despite making just 11 starts and Rashford's numbers are similarly impressive, with a goal every other start.
Mourinho has been tempted to bring Rashford in, even if that would probably mean dropping Martial or moving the France forward to the right flank to accommodate the England striker in an attacking position on the left.
Leadership challenge
One of the most frequent complaints about United last season was the lack of leadership and arrogance on the pitch.
Mourinho wasted little time addressing that, with the arrival of Ibrahimovic and Pogba helping to ease the burden on captain Wayne Rooney, while others, such as De Gea and Fellaini, have been empowered again.
United have some swagger back and look all the more authoritative for it.
Do City have the same sort of leadership?
The departure of Hart on loan, the exiling of Yaya Touré and the absence of Vincent Kompany through injury has shorn them of some of their biggest personalities and it remains to be seen in the tougher moments if they have anyone willing and able to marshal the team through difficulties.
Perhaps Guardiola's democratic style of managements encourages players to take responsibility and maybe the likes of Ilkay Gundogan, one of the summer's new signings whose debut has been delayed by injury, and Fernandinho can help carry the mantle.
Tricky business
Mourinho was not kidding when he said the absence of Agüero made it harder to predict how City will play.
"When Agüero plays, we know the formation, we know their dynamic," he said.
"Now it's more difficult. He doesn't play and they are an amazing, rich squad in terms of options."
From past experience, Mourinho may be expecting Guardiola has a trick or two up his sleeve and how the Portuguese counters that will be fascinating.
In December 2011, Guardiola memorably blindsided Mourinho by duping him into thinking he was using a four-man defence before switching to a system that involved Dani Alves pushing further forward down the right, Carles Puyol switching to right-back and Sergio Busquets operating simultaneously as a centre-half and central midfielder.
Barcelona won 3-1. United will have to be wise to any surprise Guardiola springs.
