Date, time and coverage: Wednesday 16 January, 20:05 GMT. The match will be shown live on ITV1 in the UK. You can also follow the action live via ManUtd.com’s radio and text commentary.
Form guide: United are unbeaten in eight games stretching back to December’s 3-2 league win over Manchester City, although a testing finish to Sunday’s 2-1 win over Liverpool and Sunday’s looming visit to White Hart Lane to take on Tottenham will come into Sir Alex’s thinking on selection. West Ham, meanwhile, have won just once in seven games and have registered a solitary victory on the road since October. Most alarmingly for Sam Allardyce in the context of Wednesday’s tie is that the Hammers have hit just five goals away from Upton Park this term.
Ins and outs: Ashley Young is out with a knee injury, while Jonny Evans, who missed Sunday's game with a hamstring strain, is unlikely to be risked. Nemanja Vidic suffered concussion against Liverpool but is otherwise OK. Sir Alex will use the full reach of his squad whilst handing game time to those most in need of it, namely the returning Wayne Rooney, Nani and Anderson. The Hammers have a lengthy injury list: James Collins (hamstring), Mark Noble (calf), George McCartney (knee), Joey O’Brien (hamstring), Andy Carroll (knee) and Mohamed Diame (hamstring) have all been on the treatment