The Blues take on United tomorrow at Old Trafford (4pm), which will prove critical in the title race.
Spurs closed the gap at the top again today as they thrashed Bournemouth 4-0 at White Hart Lane.
Chelsea are now just four points clear of Tottenham, although have their game in hand against Jose Mourinho’s side.
Frank Lampard says Chelsea will be looking over their shoulders at Tottenham
United have big motivation for the showdown with Chelsea as they continue pushing for a top-four finish and Champions League qualification.
And Blues legend Lampard claims his former side will be fully aware of the difficult task in hand.
The player-turned-pundit also hopes Chelsea players are nervous and transfer that into total concentration.
Manchester United v Chelsea combined XI Wed, April 12, 2017
Express Sport brings you our combined XI of Manchester United and Chelsea stars ahead of the Premier League clash at Old Trafford on Sunday (4pm)
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Who makes our combined Manchester United and Chelsea XI?
There will be some nervousness but so there should be
"Chelsea are very aware that Spurs are there and it'll be a tough game for them tomorrow," Lampard told BBC Sport.
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"There will be some nervousness but so there should be."
A win for Chelsea at United will extend their lead back to seven points with six games to go.