Having dragged themselves out of the Barclays Premier League bottom three with four consecutive victories, West Ham have lost their last two fixtures on the road as they succumbed to defeats at Everton and Stoke.
A 3-1 reverse against Allardyce's former club Newcastle in mid-January is the only home league game the Hammers have lost since the turn of the year and, with the Red Devils 12 points off the top four, the 59-year-old wants to continue a decent home run.
"Our efforts at home are what I have been focusing on with the players," he said.
"We have won the last three home games on the trot and we have to try to continue that if we can to overcome the little blip we have suffered following two away games we have taken nothing from.
"The focus is to maintain the home results and try our best to pull off a big win, but if we can't, come away with at least a point."
David Moyes has struggled to follow on from the success of Sir Alex Ferguson at Old Trafford, with United currently seventh in the table and on the back of a 3-0 defeat to bitter rivals Liverpool last weekend.
However, they will go into the game buoyed by their own 3-0 win over Olympiacos to advance into a Champions League quarter-final clash with holders Bayern Munich, and Allardyce is not taking the challenge lightly.
"Everyone is talking about Manchester United this, Manchester United that," he added.
"But in their last away game they disposed of West Brom fairly easily with a 3-0 victory. David Moyes has so many players to choose from that fatigue won't come into it because he can change the side with top international players if he wants to."
Winger Stewart Downing is hoping to inflict more misery on Moyes and his players as West Ham strive to pick up points to keep them clear of the battle for survival.
"We're not out of the water yet and we need points as quickly as we can, starting against Manchester United," he said.
"If we play to our strengths I think we can beat them. The manager will approach this game the same as any other. When they're not at their best they've still got players that can hurt you.
"We'll go through their strengths and weaknesses as a team, as we would as if it were last season. We'd love to be able to exploit their weaknesses and make sure they carry on struggling."
Allardyce has an almost fully-fit squad to choose from on Saturday with only Joey O'Brien and on-loan forward Marco Borriello missing with shoulder and calf injuries respectively.
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