We know that Ronaldo to Barca or Messi to Real madrid is never going to happen, but if we put the absolutely impossible transfers aside and if we don't take the probability too much into account, which transfers would you consider very controversial if they happened?

I'll try with a few... Neymar to Real madrid, Donnarumma to Inter and Ozil to Tottenham.

Well, obviously, any player who join a rival of its former club. Player who say they won't leave ever or claim to be very loyal to a club but end up leaving, sometime for a direct rival as well.

On some specific one:

• Ozil and Sanchez to any PL team in top 6 will obviously be controversial to a certain amount.
• Donnarumma to Inter or to Juventus (more realist atm) would no doubt anger the fan a lot.

Joey Barton to PSG.

Fredy Adu to Real Madrid

Totti to Lazio

Pique to Real Madrid, Ramos to Barcelona

Alexis to Chelsea

Didier Drogba or John Terry to Arsenal.
Marco Reus, Aubameyang or Sokratis to Bayern Munich.
Cesc Fabregas back to Arsenal. Would anger fan from both club. XD
Ciro Immobile to Roma.
Kane, Alli or Dier to Manchester United, Chelsea or Arsenal.
Icardi to Juventus or AC Milan.
Oblak, Koke, Saul or Griezmann to Real Madrid and maybe to Barcelona to a certain level.
Pepe to Barcelona or Atletico Madrid. XD

Pogba to Manchester City.

Neymar to Real is possible and might happen soon, that's definitely super controversial.

Then
Ronaldo to Chelsea.
KVD to Manchester United

Griezmann to real madrid might actually happen.

Yeah thats actually one sort of transfers I've never thought of and that could be controversial... Someone who leaves for a rival and then comes back. Fabregas to Arsenal was a good one... We've seen the controversy of such a move with Goetze. Lewandowski to Dortmund could be another one.

Anyway here are others I've been thinking of:
Cristiano to Man City
Zidane to Barca
T Muller to Dortmund
Goretzka to Dortmund
L Suarez to Man Utd

IMO players going to Inter from AC Milan isn't a big deal since it happened in the past.
Also players from german teams to Bayern since it's also a normality since Bayern is far superior to other teams there in money terms.

What I saw as real controversial was when Tevez went to Man City...the whole Manchester derby was lit, players were more passionate back then, proof is that 4:3 game.

With that in mind I would say:

De Gea to Man City...if that was to happen, fans would be into the derby game months before the actual week of the game, the hype would be huge.

@Golazo About AC Milan, Inter and Bayern, I'm not too sure, I mean, in my opinion, I'm sure those transfer alway frustrated the other team fan but it never really affected us because we follow league other than PL less. Like Neuer to Bayern must be something Schalke fan are still pretty sour about. But maybe I'm wrong, maybe some rivality are more bitter than other.

I have to agree however that any Manchester United fan would be livid if De Gea joined Manchester City. And heck, they would have a right to.

By the way, if De Gea join Real, wonder how Atletico fan would feel.

@Emo just see how many players changed from Inter to Milan or vice versa, a lot of players and many world class players as well.

Just to add some crazy transfers:

Hamsik to Juve

Diego Simeone to Real (manager)

Kane to Chelsea or Arsenal

De Bruyne to PSG

Messi to any team

Buffon to any team

@Golazo Because it happen a lot it doesn't frustate the fan anymore you mean? Strange. I would still be pissed but maybe they are chill about it. :P

Buffon to Parma wouldn't be that controversial ;)

@Emo It's really not that strange, it happened in England as well...For example when Ashley Cole went to Chelsea from Arsenal it was a big deal, fast forward a few years and it's not a big deal anymore if those clubs signed eachothers players. Inter had Ibrahimovic,Ronaldo,Pirlo and other key players that later played for AC Milan and nobody cared, fact is Ibrahimovic has always been a rent boy with a big mouth so Inter fans had mocked him but other than that nothing...

@Golazo111 Fast foward a few year and most controversial transfer aren't anymore imo. The only time it remain one is when those palyer play in a derby against the former club. Sometime even that isn't that much of a big deal anymore. Hummels to Bayern and Higuain to Juventus was extremely controversial at the time, especially for the fan who saw the player leave from their team, but obviously, it didn't seem that bad for most people who don't follow Bundesliga and Serie A. I think English rivality seem worse because it get more publicity and because its a league we have a tendency to follow more.

@Emo Yea at the start when Lewandowski joined Bayern the fans destroyed the tires of his car and then Hummels joining also made them angry but if another player was to join today the reaction would be far less dramatic since they got used to it...

About Higuain:

Here is some list of players that played for both Inter and Milan:

Luigi Cevenini: AC Milan 1911-1912, 1915-1919; Inter Milan 1912-1915, 1919-1921, 1922-1927.

Giuseppe Meazza: Inter Milan 1927-39, 1946-47; AC Milan 1940-42

Valentin Angelillo: Inter Milan 1957-61; AC Milan 1965-66

Roberto Baggio: AC Milan 1995-97; Inter Milan 1998-00

Mario Balotelli: Inter Milan 2007-10; AC Milan 2013-2014, 2015-2016

Sergio Battistini: AC Milan 1979-85; Inter Milan 1990-94

Victor Benitez: AC Milan 1962-63, 1964-65; Inter Milan 1967-68

Aldo Bet: Inter Milan 1967-68; AC Milan 1974-81

Drazen Brncic: AC Milan 2000-01; Inter Milan 2001-02

Cristian Brocchi: Inter Milan 2000-01; AC Milan 2001-05, 2006-08

Lorenzo Buffon: AC Milan 1949-59; Inter Milan 1960-63

Nazzareno Canuti: Inter Milan 1974-82; AC Milan 1982-83

Antonio Cassano: AC Milan 2011-12; Inter Milan 2012-13

Francesco Coco: AC Milan 1993-97, 1998-99, 2000-01; Inter Milan 2002-05

Fulvio Collovati: AC Milan 1975-82; Inter Milan 1982-87

Hernan Crespo: Inter Milan 2002-03, 2006-09; AC Milan 2004-05

Cyril Domoraud: Inter Milan 1999-01; AC Milan 2001-02

Maurizio Ganz: Inter Milan 1995-98; AC Milan 1998-99

Giorgio Ghezzi: Inter Milan 1951-58; AC Milan 1959-65

Andrés Guglielminpietro: AC Milan 1998-01; Inter Milan 2001-03

Thomas Helveg: AC Milan 1998-03; Inter Milan 2003-04

Zlatan Ibrahimovic: Inter Milan 2006-09; AC Milan 2010-12

Saul Malatrasi: Inter Milan 1964-66; AC Milan 1967-70

Amantino Mancini: Inter Milan 2008-10, 2010-11; AC Milan 2010

Domenico Morfeo: AC Milan 1998-99; Inter Milan : 2002-03

Adelio Moro: Inter Milan 1972-75; AC Milan 1981-82

Pierluigi Orlandini: Inter Milan 1994-96; AC Milan 1999-00

Christian Panucci: AC Milan 1993-96; Inter Milan 1999-00

Giancarlo Pasinato: Inter Milan 1978-82, 1983-85; AC Milan 1982-83

Giampaolo Pazzini: Inter Milan 2011-12; AC Milan 2012-2015

Andrea Pirlo: Inter Milan 1998-01; AC Milan 2001-11

Luis Nazario Ronaldo: Inter Milan 1997-02; AC Milan 2007-08

Andrea Poli: Inter Milan 2011-12; AC Milan 2013-2017

Nevio Scala: AC Milan 1967-69, 1975-76; Inter Milan 1973-75

Clarence Seedorf: Inter Milan 2000-02; AC Milan 2002-12

Aldo Serena: Inter Milan 1978-79, 1981-82, 1983-84, 1987-91; AC Milan 1982-83, 1991-93

Matias Silvestre: Inter Milan 2012-13; AC Milan 2013-2014

Dario Simic: Inter Milan 1999-02; AC Milan 2002-08

Davala Ümit: AC Milan 2001-02; Inter Milan 2002-03

Patrick Vieira: AC Milan 1995-96; Inter Milan 2006-10

Taribo West: Inter Milan 1997-99; AC Milan 1999-00

Chedric Seedorf: Inter Milan 2000-2011; AC Milan 2008–2009

Sulley Muntari: Inter Milan 2008-2011, 2011-2012; AC Milan 2012-2015

Leonardo Bonucci: Inter Milan 2005-2007; AC Milan 2017

@Golazo Like I said, I didn't argue it happened a lot, I just tought that maybe some of those transfer must have been frustrating for the fan. Lets say Chelsea sold tons of player over the time to Arsenal in the past, I'm sure it wouldn't change the fact you would be angry if Hazard just ended up joining them next season. Thats was the only point I was trying to make. Sure it happen a lot between AC and Inter, but something happening a lot doesn't make it less frustrating, especially if its key player. If Icardi joined AC Milan, wouldn't matter how many transfer between the two club there been in the past. It would cause uproar for Inter Milan fan for sure!