Glenn Whelan is also out, with the midfielder pulling a calf muscle after replacing Sidwell at Anfield.
The duo join four others injured in Victor Moses (thigh), Robert Huth (calf), Peter Odemwingie (knee) and Dionatan Teixeira (broken foot), but defender Phil Bardsley is available again after missing the match on Merseyside through illness.
Manchester United provisional squad: De Gea, Lindegaard, Amos, Vermijl, Rojo, Smalling, Blackett, Thorpe, McNair, Pereira, Fletcher, Valencia, Lingard, Fellaini, Anderson, Carrick, Young, Herrera, Mata, Januzaj, Falcao, Rooney, Van Persie, W Keane
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