The summer transfer window shuts at 11pm on Friday, with the U’s welcoming North End for a Sky Bet Championship clash on Saturday.
A striker, plus potentially a centre back, are the two positions that United are most likely to prioritise over the course of the next few days, while there will probably be outgoings for those currently on the periphery of the squad.
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Asked about Friday’s deadline, and what the ideal situation would be, U’s head coach Buckingham said: “I’d love to have them in before 11pm on Friday, but I suppose we’ll just have to wait and see what is possible.
“The earlier the better because it allows us to plan potentially for the weekend, but if it goes down to the wire to get what we want, then so be it.”
United have already signed 14 players this summer, with goalkeepers Jamie Cumming, Matt Ingram and Jacob Knightbridge, full backs Jack Currie, Peter Kioso and Hidde ter Avest, midfield trio Idris El Mizouni, Louie Sibley and Will Vaulks, wingers Malcolm Ebiowei, Marselino Ferdinan, Matt Phillips and Przemyslaw Placheta, and striker Dane Scarlett all joining the club.
Crystal Palace wide man Ebiowei and Tottenham Hotspur centre forward Scarlett are the only two players to have joined the U’s on loan so far.