The West Ham boss believes that Sir Alex Ferguson's Red Devils could finish on an unprecedentedly large points tally as they close in on another Premier League title.
Sir Alex Ferguson's men are 15 points clear of nearest rival Manchester City and would break the division's record points tally if they win all of their remaining games, leading the Hammers boss to hail the Red Devils vintage as possibly their best ever.
"I think you have to say the United team is as good as it has ever been because nobody normally wins the title so easily and by so big a margin, or has this much of a margin at this stage of the season," Allardyce told reporters.
"It is pretty scary what total they might actually finish with. They have been outstanding and their squad rotation has been Sir Alex's masterpiece, as usual - about playing the right team at the right time."
The 58-year-old feels that United's early exits from other competitions were a big factor in helping them surge to what is set to be its 20th English crown.
"They have not had the normal focus on three or four competitions almost to the end - the focus has come on the Premier League, and they have just breezed it - everyone else can't get near them," he observed.
"We will need to be on our best form, as always, if we are to get anything but we have run them close three times this season.
"I would say we are still another couple of points off being absolutely safe. Hopefully we can win a couple of matches and see where we go."