Saturday's testing trip to West Ham means an early kick-off and the chance to move eight points clear at the top but it's certain to be a difficult examination against Avram Grant's side.
Arsenal, who entertain Blackburn on Saturday, are five points behind United, but with a game in hand and the blockbuster showdown at the Emirates Stadium still to come.
Sir Alex believes the Gunners are the biggest threat to the Reds' bid to lift a record 19th league title but has refused to rule out a late challenge from three other contenders.
"It looks as if it's going to be us and Arsenal," he told Inside United. "But you never know.