It's fifth versus sixth going into the weekend - and Arsenal surely need a victory to keep their Champions League hopes alive. Michael Cox assesses the tactical battle, and Alan Thompson finds some promising bets...
"It's still very peculiar to see Arsenal odds-on against a Manchester United side unbeaten in 25 league games."
Arsenal v Manchester United
Live on Sky Sports 1
Match Odds: Arsenal 1.981/1, Man Utd 4.3100/30, The Draw 3.814/5.
Arsenal and Manchester United are still battling for a Champions League place - but whereas United will qualify for that tournament with a Europa League triumph, Arsenal only have the league, and must surely win this game to have any chance.
Indeed, the Europa League will be in the forefront of Jose Mourinho's mind here. He's set to make plenty of changes from the side which defeated Celta Vigo 1-0 on Thursday evening, saying that the players who have played the most number of minutes since the start of April will be those sacrificed here. It remains to be seen whether that statement rings true, however.
The focus here, though, is on Arsenal. Fail to win and it's difficult to imagine how the Gunners can maintain Arsene Wenger's amazing record of finishing in the top four every year since taking charge of Arsenal in 1996. There are many question marks about his probable formation and starting XI here.
Wenger has used a three-man defence for the last four matches, but in the last two - a win over Leicester and a defeat to Tottenham - he's switched to a back four in the second half, and it seems likely that he'll start with a four-man defence here.
The return of Shkodran Mustafi should see him start alongside Laurent Koscielny - Gabriel had a difficult game against Tottenham - with Hector Bellerin returning on the right and Nacho Monreal on the left. The three-man defence, meanwhile, would probably see Bellerin missing out and Alex Oxlade-Chamberlain continuing as right-wing-back.
Granit Xhaka looks set to miss out through injury which means Francis Coquelin starting in holding midfield, allowing Aaron Ramsey to make forward runs into attack.
Further forward, Mesut Ozil and Alexis Sanchez will definitely start, although it remains to be seen in which roles. Sanchez has been fielded on the left and upfront, while Ozil could start as a number 10 in a 4-2-3-1 or either to the left or to the right in the 3-4-3. In truth, it's difficult to see precisely what Wenger is trying to achieve in the final third at the moment.
Olivier Giroud was poor against Tottenham and Danny Welbeck will surely be handed a start here against his former side. He offers more pace in the channels, and can play as a traditional centre-forward when Arsenal get the ball wide too.
Manchester United's team selection is anyone's guess. There are still major injuries at centre-back, although at least Chris Smalling emerged from the bench for the final couple of minutes in Vigo, suggesting he'll be fit to start here.
Michael Carrick may return in the holding role, Juan Mata could start on the right and Wayne Rooney - who has such a fine record against Arsenal - could play either as the number 10 or upfront. Anthony Martial is another likely to come into the side, probably in a relatively rare centre-forward role.
United may struggle to cope with players between the lines here, with both Ozil and Sanchez floating in that zone, and it remains to be seen how effective their transitions are. The speed of Martial, however, could give Arsenal serious problems.
Arsenal haven't been impressive in possession in recent weeks and their most dangerous midfielder might be Oxlade-Chamberlain, depending upon which role he's fielded in - he might be pushing forward from wing-back, deployed in a more central position in the absence of Xhaka, or perhaps even in his old right-sided midfield role. He's often been Arsenal's liveliest performer in recent weeks, however, regardless of his position.
Mourinho might be resting players, but it's still very peculiar to see Arsenal odds-on against a Manchester United side unbeaten in 25 league games. I'll lay Arsenal at that price.