Mesut Özil's time at Arsenal looks likely to come to a turbulent end, as the German is no nearer to signing a new contract at the Emirates. And something that will make his departure even more bitter to Gunners fans is that a reunion with Jose Mourinho at Manchester United could be on the cards.
Özil played under Mourinho at Real Madrid, where the Portuguese manager compared him with Zinedine Zidane because of his creative abilities. The German is also apparently interested in a move back to Madrid, or to their fierce rivals Barcelona, as he looks to leave the Gunners in search for silverware.
And with the 28-year-old interested in a switch to Old Trafford, here's a look at the top five players to transfer to rival clubs.
1. Sol Campbell
Sol Campbell's decision to move from Tottenham to Arsenal wasn't exactly met with cheers from those at White Hart Lane. The former England centre-half was adored by the Tottenham faithful, but he was searching for a new challenge and the chance of competing in the Champions League, which most Spurs fans could understand. But for the defender to move to bitter rivals Arsenal, and for free, was unforgivable.
Campbell unsurprisingly received a horrendous reception and developed a new nickname at White Hart Lane - Judas.
Campbell won two Premier League titles, three FA Cups and appeared in a Champions League final, justifying his decision to stay in North London. Clinching the Premier League title in 2004 at Spurs didn't exactly silence the boo boys, however.
2. Luis Figo
Arguably one of the greatest of all-time, Luis Figo also has another nickname by many in Catalonia - traitor. His transfer to Real Madrid was made even worse by the fact he was beloved by all at Barcelona, winning two La Liga titles and two Copa del Rey's during his time at the Nou Camp.
Figo went on to enjoy similar success at the Bernabeu, including earning a Champions League medal in 2002. However, when Figo returned to the Nou Camp, he was subject to all kinds of abuse - including having a pig's head thrown at him.
3. Ashley Cole
'Cashley' Cole - Arsenal's former left back.
Cole performed many u-turns during a series of tapping-up meetings and big money offers to eventually end up at Chelsea - a move that turned out to be the best for him in terms of silverware. The full-back signed a contract extension at Highbury before switching to Chelsea soon after, claiming he was insulted by the low amount Arsenal had offered him.
And despite Cole having the cheek to claim he had forgiven Arsenal for "hanging him out to dry", Gunners fans are far from forgiving.
4. Carlos Tevez
Carlos Tevez has dragged drama with him wherever he's been, so there's no surprise he decided to switch from Old Trafford to the Etihad. The Argentine was adored at United for his hard-working experience and contribution, helping his side win two Premier League titles and one Champions League during his two years at Old Trafford.
However, a switch to City was controversial from the start, with the club erecting a blue 'Welcome to Manchester' billboard with Tevez the main feature, causing a stir amongst the rivals. In hindsight, the Red Devils will be glad he was no longer on their books, as Tevez created unrest within the City dressing room, refusing to come on as a substitute in their away tie against Bayern Munich in the Champions League.
5. Emmanuel Adebayor
Emmanuel Adebayor will be remembered for a wonder-strike against Spurs during a 3-1 win at White Hart Lane and, rather less favourably for Arsenal fans, his pitch-long sprint to celebrate in front of the Gunners while at Man City. The Togo international made his switch to City, where he enjoyed a fine two-years at the Etihad.
However, if he wasn't already dead to Arsenal fans, his switch to Spurs to 2011 would be the final nail in the coffin. He went on to make 92 appearances in four years at White Hart Lane, although he failed to win any honours with either London side.