Just four points separates first from third, United and the Gunners have seven games to play, the Blues have eight. Yet it could be events off the field which have a greater say on the destination of this year's championship.
All three clubs have injuries to key players.
ARSENAL The worry that Arsenal's season could flounder after the injury suffered by Robin van Persie in November has proven unfounded.
Arsene Wenger has been helped by the returns of Theo Walcott, Nicklas Bendtner and Tomas Rosicky. But his biggest boost may yet still come, one which may swing the title in his favour.
Robin van Persie
The Dutchman seriously damaged his ankle ligaments while on international duty back in November, an injury which initially threatened to end his season and wreck his World Cup chances.
Ready to return: Robin van Persie could give Arsenal a major boost in their pursuit of glory
But he has revealed he has already been training with a ball for several weeks and although still some way off full fitness, he is hoping to return in time to help the Gunners seal a Premier League and Champions League double.
Chance of return: 6/10
'An endless problem' is how Wenger has described Gallas's calf strain. An injury which has thrust his 35-year-old replacement Sol Campbell into the limelight.
Campbell is playing a much greater role than he could have envisaged when he re-joined the Gunners back in January - he has appeared in five of the last seven games.
Case for the defence: Gallas will be out of action for at least another fortnight
And the veteran defender is sure to be tested to the limit in the Champions League clashes with Barcelona.
Absent for six weeks already, Gallas isn't expected back for at least another fortnight.
Chance of return: 7/10
CHELSEAThe Blues' dip in form has seen the one-time title favourites drop off the pace, winning just two of their last six games.
The most worrying aspect of the run is just how shaky Carlo Ancelotti's side have been at the back.
John Terry's drop in form after his well-publicised philandering has been compounded by injury to key players, mainstays of Chelsea's defence.
Losing a player who is, arguably, the best left-back in the world would trouble any club and it seems likely Chelsea won't see Cole again this season.
Big blow: Chelsea have clearly missed Ashley Cole
In excellent form until his clash with Landon Donovan at Goodison Park - in which the defender broke his ankle - the Blues are now relying on second and third-choice players to fill the gap. And it shows.
Chance of return: 3/10
It all looked rather innocuous at first, as Cech signalled to come off during the Champions League defeat to Inter Milan back in February. But his injury has sidelined him for a month now and his replacements have struggled.
Cech: Picked up an injury during Chelsea's Champions League clash with Inter Milan in Italy last month but should be fit to face Portsmouth
Hilario was beaten too easily twice when Manchester City beat Chelsea 4-2 and Ross Turnbull has been left exposed in his two appearances, neither of which Chelsea have won.
But the prognosis couldn't be more promising for Carlo Ancelotti, with Cech reported to be fit for Chelsea's clash with Portsmouth on Wednesday night.
Chance of return: 10/10
MANCHESTER UNITEDSir Alex Ferguson has had to deal with a number of injury worries right all through this season. From the permanently sidelined Owen Hargreaves to Rio Ferdinand and his troublesome back, Fergie has had to put out a patched-up squad on a number of occasions.
But the depth of United's squad has ensured they remain title contenders, despite a list of injuries which would have scuppered smaller side's chances.
However, with just seven games remaining for United, there is one problem that could sink their title hopes.
Sir Alex's side are in the hunt for their fourth straight championship, thanks largely to the form of Wayne Rooney.
Catch me if you can: Rooney celebrates after scoring against Liverpool on Sunday
Rooney has scored 32 goals in all competitions this season and picked up the slack left by the departure of Cristiano Ronaldo. But he is a doubt for Manchester United's trip to Bolton on Saturday because of his ongoing knee problem.
And with a clash against Chelsea and two Champions League matches with Bayern Munich just around the corner, United will be hoping their talismanic striker's injury is no more than a niggle.
Chance of return: 9/10
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