Who has the most to lose? On the weekend that the Big Four go to war, there is one man whom defeat will damage the most. He has tried to face down the discontent within his own club; now Jose Mourinho will have to make the decision that could define Chelsea's season.
This time it will not all be about whether he picks Andrei Shevchenko, although his inclusion will be a cause for debate. Instead, it will be whether Petr Cech starts in goal for Chelsea against Liverpool for the first time since 14 October with a metal plate protecting his skull. The indications last night were that Cech will be in goal at Anfield this lunchtime with the adapted rugby headguard that he must wear for the next three years of his career.
Some match to walk back into after surgery on your skull. Some state for his club to be in. As Cech sipped tea in the House of Commons this week with his team-mates, Chelsea's squad may have looked becalmed but there is no doubt that the players have been aware of the fissures within their club. It may only be six points separating themselves from Manchester United but today has come to represent a great deal more for Mourinho.
If John Terry is not passed fit, how does he cope with the threat of Peter Crouch? If Cech is truly ready then is he also ready for the blood and thunder of Anfield? And what of Shevchenko, whose presence takes on a symbolic status in the disagreements with the board? In May 2005, Roman Abramovich watched a Champions' League dream go up in smoke at Anfield. Will today be just as significant in the modern Chelsea era?
Michael Ballack said that it would be in the "big games" that Chelsea would show their true selves this season. "There are moments during a season that are crucial, that if you lose games it becomes difficult and if you win it's easier," he said. "Maybe now is a big moment when the big decisions will be made. This weekend could be a big turning point. We could go to three points, stay at six points or go out to nine. We don't want to lose points as the distance would be too big, but it's difficult for both us and Manchester United."
United's £20m bid yesterday for Ballack's former Bayern Munich team-mate Owen Hargreaves will have told Chelsea everything they need to know about the resolve of the Premiership leaders to win Sir Alex Ferguson's ninth title. It is a bold move that announces that the old guard of this division will pay the price, however extravagant, for the players they believe can deliver them a title. An offer of £20m for a holding midfielder? It has the decadence of an Abramovich signing but it reasserts United's power and intent.
It may just be all the encouragement that the unusually reluctant Chelsea board needs to buy Mourinho his new defender this month.
In the mean time, Ferguson can point to another advantage that his opposite number lacks. There is not an injury among the United players, unless you count Ferguson's reservations about Alan Smith. This time, the Scot's team are not the embattled strugglers closing in on the title: they have a rare sense of calm about them.
The last time United won the title, four years ago, they were five points behind Arsenal with 15 matches to play. This time Ferguson has the luxury of being able to consider whether or not Arsenal, his opponents tomorrow at the Emirates Stadium, are realistically even outside contenders for the Premiership title.
"You can never say it completely [that Arsenal are out] - I think the most important thing is ourselves," he said. "We've got to try to keep a consistency from now until the end of the season that helps us win the League.
"It is going to be consistency that decides it, no question. Our form is good but there have been examples of us being charitable at West Ham and Newcastle, and these are danger signs for us. We have to make sure nothing like that happens over these last 15 matches."
It is the sixth of Rafael Benitez's Premiership meetings with Jose Mourinho today and, if he is to present any sign of progress to Anfield, then the Liverpool manager cannot lose this one like he has the other five matches.
"The victory over Watford last weekend has not taken the edge off the smarting wound of the manner of Arsenal's 6-3 Carling Cup quarter-final win. If there ever was a time to beat Mourinho's Chelsea then surely it is now.
"We know we need to improve against the top sides, it's clear we can do it, we have the confidence to do it," Benitez said. "In the Champions' League, in the cups, we can beat them but we also need to take our chances before they do. If we scored first against the top teams, it would be a different game.
"It doesn't guarantee you will win, but you can control the game more if you score first."
There have been slips in the Premiership for Manchester United this season, against West Ham United most notably, but only one team can truly claim to have embarrassed them.
Ferguson had the good grace to recall the defeat to Arsenal at Old Trafford in September with the acknowledgement that Arsène Wenger's team were the "far better side". And it was that result that has sustained the Arsenal manager's faith in his young side.
"In our mind it's a game that we want absolutely to win, I tell you," Wenger said. "We love to win. We want to reduce the gap to Manchester United as quickly as possible and we want to continue our run because we're in good form. We're involved in nearly every competition, even the championship, and you never know."
In fact, Wenger said that after beating United in September that he never expected that Sir Alex Ferguson's side would be 15 points ahead in the Premiership come January.
There was a time when that might be have been seen as a touch provocative but what was once the most intriguing rivalry in football is not the weekend's potentially most spectacular act.
That will be Mourinho, his mood come this afternoon and whoever he chooses to battle with next.
Two players who have something to prove at the Emirates Stadium tomorrow
By Glenn Moore
Gilberto Silva has been one of Arsenal's key players this season - according to some pundits and statistics the key player - but the Brazilian World Cup winner is suspended for tomorrow's match having been sent off against Blackburn at Ewood Park last weekend. In his place will be the versatile Frenchman Mathieu Flamini.
Signed amid controversy from Marseilles in 2004, Flamini, 22, has been a reliable performer for Arsenal without being able to nail down a regular place. Following his impressive display against Liverpool in November, this is another opportunity for him to show he is the natural heir to the 30-year-old Gilberto as Arsenal's midfield enforcer alongside Cesc Fabregas. There is plenty of competition for the role, as Fabrice Muamba's form on loan to Birmingham has demonstrated.
* MICHAEL CARRICK
The £18m summer signing has gradually established himself as a significant presence in the Old Trafford midfield, even scoring recently. Yet there remains a sense that he does not command a game to the extent his talent suggests he should. Tomorrow he will be in direct comparison to Cesc Fabregas, Arsenal's extravagantly gifted Spanish youngster. It is an opportunity for the 25-year-old Geordie to argue his case for a central role in the England team. It is also, with Owen Hargreaves on Sir Alex Ferguson's shopping list, a chance to prove he has the personality to be at the heart of the United midfield for years to come.
Carrick was for a long time a target of Arsène Wenger, but despite playing well against the Gunners, he has never been a winner against them, for West Ham, Tottenham, or United, yet.