Jose Mourinho and Arsene Wenger to renew long-standing rivalry
When Manchester United faced Manchester City last week, many eyes were watching the sidelines for any flaring up of the toxic rivalry between Jose Mourinho and Pep Guardiola.
But while that game passed without incident, and it appears those two old adversaries have - at least temporarily - called a truce in their long and bitter feud, there is one Mourinho quarrel that rarely seems to go quiet.
It concerns the long-serving Arsenal boss Arsene Wenger and dates back much further than the Guardiola squabble of the last seven years. The United manager has been at odds with the Frenchman for more than a decade, describing him as a "voyeur" and a "specialist in failure" in some of his more memorable put-downs.
It is a battle in which Mourinho has often held the upper hand, and on the pitch it was not until their 14th clash that Wenger finally got the better of the Portuguese.
Wenger, however, has seldom shirked the verbal challenge and there was once a physical confrontation on the touchline.
As the pair meet again at the Emirates Stadium on Sunday, the potential for another fall-out in their sour relationship clearly exists. It may not be a winner-takes-all title clash but it is nevertheless a game of huge importance, with Champions League qualification on the line.
The pair locked horns for the first time after Mourinho took charge of Chelsea in 2004. Mourinho took unkindly to comments from Wenger criticising Chelsea's lack of homegrown players and their tactics.
"Wenger has a real problem with us and I think he is what you call in England a voyeur," said Mourinho, ramping up the fight. "He is someone who likes to watch other people... He speaks, speaks, speaks about Chelsea."
From there it exploded as Wenger accused Mourinho of being "out of order, disconnected with reality and disrespectful".
He added: "When you give success to stupid people, it makes them more stupid sometimes and not more intelligent."
Mourinho responded by claiming he had compiled a 120-page file of quotes from Wenger about Chelsea.
The verbal blows have been traded ever since. Even after Mourinho left Chelsea for Inter Milan and Real Madrid, there were comments criticising each other's tactics or teams.
When Mourinho returned to Stamford Bridge for a second spell, Wenger questioned the timing of Chelsea's sale of Juan Mata to Manchester United in 2014.
"Chelsea have already played twice against Man United," said Wenger, whose side still had to play United. "I think if you want to respect the fairness for everybody, this should not happen."
As the title battle heated up that spring, with Arsenal strongly in contention, Wenger claimed his rival managers were consistently talking down their chances because of a "fear to fail".
Mourinho seized upon this with a remarkable broadside.
He said: "Am I afraid of failure? He is a specialist in failure. I'm not."
To underline the point, Mourinho then ruined Wenger's 1,000th Arsenal match as Chelsea thrashed the Gunners 6-0.
In October 2014, the pair clashed physically when Wenger shoved Mourinho in a touchline spat. A year later there was no post-match handshake at the Community Shield after Wenger's Arsenal beat a Mourinho side for the first, and so far only, time.
Since then Mourinho has continued to aim sly digs at Wenger. He has repeatedly suggested he is treated far more harshly than the Frenchman by authorities when it comes to disciplinary matters.
With the stakes high this weekend, there is a feeling it may not take much on either side for the bad blood to spill over again.