Clearly, Arsene Wenger and Juergen Klopp have made quite an impression on each other. The Arsenal manager describes the work of his Dortmund counterpart as "exceptional"; the German states that "Arsene Wenger football" is, for a supporter, "the most beautiful style you can watch".
Part of the reason for such effusive praise might be that there's also considerable empathy there too. More than pretty much anyone else in football, Wenger will have known exactly how Klopp was feeling on that now notorious day when it was announced Mario Goetze was leaving Dortmund for Bayern Munich. "We have gone through that," Wenger acknowledges. "It hurts."
It is also one of the standout strands to the Champions League fixture at the Emirates on Tuesday, particularly given how it may point to their capability of competing for this season's trophy. Arsenal and Dortmund are probably the two biggest clubs in Europe to have been forced into the most unwanted and undue sales. It hurts all the more because both Klopp and Wenger are such project builders, always with an eye on the long term. Just when they have seemed set to make a significant next step, a departure has abruptly hauled them back.
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It is probably there, however, where the similarities start to end. Wenger explained a key difference when asked about the exits both clubs have suffered.
"We have a style of play that is worked inside the club," the Arsenal manager said. "We have many players that have been educated here, who form our team. Dortmund have created a style with plenty of players they bought, but they bought with very intelligent scouting. So they have done it in a little bit different way but as well not in the most expensive way, so they deserve a lot of credit."
Dortmund also deserve credit for the way they have reacted. Indeed, it is that contrast in fundamental team-building that arguably explains why Klopp has been able to respond to so many negatives in a more positive way. Whereas Arsenal's first high-profile departures saw them begin to leave Champions League qualification later and later, to the point it seemed like the line would rise and finally leave them out, Dortmund went and won a second successive title and then reached the Champions League final.
Many around Arsenal's London Coleny training base explain that Wenger's entire process is based on gradually developing understanding and integration, as he stated on the eve of the game. So, when a key player departs, it badly disrupts the chemistry and thereby affects their confidence and cohesion. Klopp's hectic high-energy approach does not quite require the same degree of familiarity, allowing new players to more readily fit in.
"Basically the structure of the team and the quality of the team is similar," Wenger says.
An individual who almost illustrates the entire issue sat beside the Dortmund coach at the Emirates on Monday. Nuri Sahin stated that it didn't take that long to get back up to speed with the German side's approach, despite a difficult and disappointing year and a half away from the Westfalonstadion after deciding to join Real Madrid in the summer of 2011. "The team developed as well as the players," Sahin said. "It took not that much time."
A further factor might be that the issue goes beyond the technical, to the emotional. It is not just the confidence of the players that is affected with Arsenal. Wenger has previously admitted that every such departure affected him deeply, and had taken him a while to get over. Klopp has consistently displayed a much more rational approach, and he did so again on Monday.
"It is not important to think about the players you lose. It is important to think about the players you have. Mkhi [Henrikh Mkhitaryan], Auba [Pierre-Emerick Aubameyang], Sokratis, [Erik] Durm -- in the future you will know them. These are part of the new team. You have to try to get better each day."
Whereas Wenger has tended to dwell on setbacks for longer, Klopp has tried to deal with them and get on with it. The reaction to the Goetze news was a case in point, as Dortmund went and dismantled Real Madrid in the Champions League semifinals. And yet, on the eve of their match, it is Arsenal that Klopp praises as "favourites" for the contest, and Wenger's side that are currently being praised for their football.
Of course, that may be precisely because the London outfit did not lose anyone significant this summer. Similarly, the signing of Mesut Ozil arguably proves the point. Klopp argues that it was not just that Wenger finally brought someone big -- it was who they bought and how he fits in.
"I think this team missed one player, and maybe this can be Mesut Ozil," Klopp claimed. "I think he has everything. You don't have to force him in training. Just natural. It works very well. That's why it was a great idea for Arsenal, and not so great idea from the club that let him go.
"I have the impression that [Arsenal's] style has always been modern, and now it is working well with the right players at the right time. Now, one year after Van Persie, Arsenal are back, playing much more flexible. That's Arsene Wenger football. I like this. When I watch as a football supporter, this is the most beautiful style of football you can watch. Now they are back in the race and we want to stop them."
Arsenal will also have to stop Dortmund's lightning attacks, even if the German side have stuttered lately. Klopp concedes that it will likely be the home side who dominate the ball, but that does not necessarily mean dominating the scoreline. There is also the fact that, for all Arsenal's excellent football, this game is the first of a difficult spell that will reveal how good they really are.
A victory that would virtually guarantee qualification for the knockout stage would be the perfect way to start proving a point, especially on Wenger's 64th birthday. He claims he has never been one for celebrating it: "Just for me, a good game is the best present."
That is what many are expecting. Klopp, who has to sit in the stands as a result of a suspension from the Napoli game, says he would "pay for a ticket". And that despite so many other clubs paying for these teams' best players.