Supporters of Arsenal and Tottenham are well aware of the hostility that can be created when a player moves between two intense local rivals. The 1,000 Arsenal followers travelling to Belgrade for Tuesday's Champions' League tie against Partizan will therefore appreciate the emotions provoked by their opponents' Brazilian striker Cleo, who in the summer of 2009 switched from one of the Serbian capital's two biggest clubs, Red Star, to the other, Partizan.
Sol Campbell had it easy in comparison, for Red Star's most fanatical fans can be excitable chaps; their infamous set-to with Dynamo Zagreb's ultras in 1990 is commemorated at the latter's stadium in a monument dedicated to "fans of this club who started the war with Serbia at this ground".
In the "war without the shooting" (George Orwell) that is this sporting life, Cleo's transfer broke new ground as the first between Red Star and Partizan for more than 20 years. He had only been on loan to the former from his Brazilian club, but had quickly become a popular figure, and in switching to the rivals who had just beaten Red Star to the league title he provoked an outcry that included death threats.
Partizan supporters, regarding him as the enemy, were slow to warm to him as well, until a rush of goals caused a thaw. He believes the key moment was scoring in a win over Red Star that helped propel his new club towards their third successive title, remaining unbeaten all season. "It was really difficult at the beginning," he said. "The atmosphere wasn't good. Scoring that goal was the way I conquered the hearts of Partizan supporters."
The new season has been even better personally, starting with another flurry of goals that earned qualification for the Champions' League group stage for the first time since 2003 (when Partizan knocked out Newcastle on penalties). Cleo scored in every one of six qualifying ties, giving him a total of 14 goals in 15 European games, even though the side as a whole did poorly in last season's Europa League. Limited ambition, he says, is now being superseded by greater self-belief: "At first the main objective was just to get to the main draw and maybe to finish third in the group. But the way we've been doing, we're starting to dream a bit more. It's surprising even to us to have lost only one game but we're a very strong group, very united."
That defeat was in the opening Group H game, 1-0 away to Shakhtar Donetsk, after which they learnt that Arsenal had demolished Sporting Braga 6-0. It was a result that confirmed Cleo's respect for the London club. "We're always watching the Premier League on television in Serbia and I like watching Arsenal. The way they play, it's almost Brazilian. It's a great style and I like the way Arsène Wenger gives opportunities to young players. I'm very fond of Cesc Fabregas, [Andrey] Arshavin and the [Marouane] Chamakh guy. It will be an honour to play against these guys. After what they did to Braga, I'm a bit worried, but I think our supporters will make it difficult for Arsenal."
Partizan's first-choice goalkeeper is Vladimir Stojkovic, who spent last season at Wigan Athletic, though he played only four league games. Cleo says, however, that with English football so widely available in most countries, "there are no secrets about how they play. You don't need to ask people, we see so much of them".
Other team-mates that he suggests Arsenal will need to be wary of in a team comprising a mix of youth and experience are three midfielders: Sasa Ilic, the Serbia international who scored more than 100 goals in his first spell at the club from 1996-2005; Radosav Petrovic, a 21-year-old who appeared briefly at the World Cup; and Nemanja Tomic, 22, who was in Radnicki's first team aged 16.
Cleo may yet become another Serbian. Despite being in the country for only two years, he has received a special fast-track invitation from the prime minister to take dual-citizenship, which would enable him to play. "If Brazil came for me I would not think twice but I have to consider the possibility to play for Serbia."
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This week's other European ties
Champions' League: Chelsea v Marseilles (7.45pm, Sky Sports 2)
The popular Didier Deschamps returns to Stamford Bridge in charge of a team that won the French League for the first time in years, only to suffer an anti-climax at the start of this campaign. At home to Spartak Moscow they disappointed 54,000 fans by losing to an own goal in the last 10 minutes.
Champions' League: Rangers v Bursaspor (7.45pm, Sky Sports 4)
First meeting of the two outsiders in Group C, in which Rangers can take heart from the results a fortnight ago. While they were holding Manchester United by parking a fleet of buses in front of goal, the Turkish champions lost 4-0 at home to Valencia.
Champions' League: Valencia v Manchester United (7.45pm, ITV1)
Despite selling David Villa, David Silva and Nikola Zigic last summer, Valencia shot to the top of the Spanish League last weekend with a third straight win. Roberto Soldado, signed from Real Madrid, is now their main striker.
Europa League: Manchester City v Juventus (8.05pm, Five)
Billed as a glamorous tie, although Juve, seventh in Serie A last season and mid-table this time, are hardly the force of old that Roberto Mancini used to encounter. That was illustrated when they were held 3-3 at home by Lech Poznan in their opening match.
Europa League: Utrecht v Liverpool (6pm, ITV4)
The rather flattering 4-1 win over Steaua Bucharest was Liverpool's best result of the season, though Roy Hodgson will find that Europa League results do not compensate for domestic deficiencies. Utrecht drubbed Celtic 4-0 and began the group by drawing 0-0 away to Napoli.