Neither club have flexed their muscles in the summer window yet and now only have until 11pm on Monday night to add to their respective squads.
Having been linked with a host of big-name midfielders, new United boss David Moyes has ended up missing out on Barcelona playmaker Thiago Alcantara, who moved to European champions Bayern Munich instead, and another Barca star Cesc Fabregas, who opted to stay and fight for his place at the Nou Camp.
The club have also been linked with Real Madrid's Luka Modric and Daniele De Rossi of Roma as they aim to improve the squad for the remainder of the campaign.
Moyes could still return with an improved offer to former club Everton for left-back Leighton Baines and midfielder Marouane Fellaini, and Athletic Bilbao's Ander Herrera has been another late target, although his club coach Ernesto Valverde does not envisage the youngster leaving Spain.
Arsenal have also struggled to add to their squad despite chief executive Ivan Gazidis making clear at the end of last season that money was available to strengthen the team.
So far only Yaya Sanogo and Mathieu Flamini have arrived at the Emirates Stadium on free transfers, with the club having failed to push through deals for Real Madrid forward Gonzalo Higuain, who moved to Napoli instead, Liverpool striker Luis Suarez or Bayern Munich defensive midfielder Luiz Gustavo.
Newcastle midfielder Yohan Cabaye could yet make the move to north London and there is still time for deals to be struck for the likes of Real Madrid duo Karim Benzema and Angel di Maria.
There remain several other clubs who are still looking to strengthen over the course of the next 24 hours.
Liverpool had a trio of players present at Anfield for their match against Manchester United, with all three expected to pen deals with the Reds.
Victor Moses is set to join on a season-long loan from Chelsea with defenders Tiago Ilori and Mamadou Sakho ready to sign from Sporting Lisbon and Paris St Germain respectively.
Chelsea appeared to have finished their business with the signing of Samuel Eto'o from Anzhi Makhachkala, but manager Jose Mourinho is reported to be keen to add further depth to his striking options in the final hours of the window.
Crystal Palace have made 11 signings but manager Ian Holloway still wants to add another four or five players as he looks to build a squad deemed capable of ensuring survival.
The Eagles beat Sunderland 3-1 on Saturday, with Black Cats boss Paolo Di Canio also stating a desire to add to his ranks.
Newcastle have been much quieter than their north-east rivals so far, with Loic Remy's loan move from QPR the only deal completed by new director of football Joe Kinnear.
Norwich have spent more this summer than ever before but Chris Hughton is still eyeing a move for a winger whilst an experienced Premier League striker is Steve Bruce's main target for Hull. Jermain Defoe and Demba Ba are continually linked with loan moves away from their clubs, with West Brom in the hunt for a forward.
Defoe's former club West Ham look to have finished their transfer business early while the likes of Aston Villa, Cardiff and Swansea could also have a relatively quiet time of it on deadline day. In the Sky Bet Championship, QPR boss Harry Redknapp has stated his intention to add further strength to his already well-equipped squad as they aim to bounce straight back to the top flight.