Leaders United moved six points clear of City with a 3-2 win at the Etihad Stadium and the manager has challenged his players to still be top at the turn of the year.
Sunderland’s visit on Saturday is the first of five league games in 18 days for the Reds, culminating in a trip to Wigan Athletic on New Year’s Day.
Sir Alex is hoping his squad does not suffer too many injuries in that period, as happened in the 1997/98 season, when the Reds were 13 points clear of Arsenal on Boxing Day, but ended up losing the league to the Gunners by a point.
“I'm happy with six points and it's City's challenge to try and catch us,” he said at his Friday press conference.
“There are a lot of big games to come and I don’t think six points is such a healthy lead. We threw a league away against Arsenal years ago, in 1998.
“We had a catalogue of injuries and that is the key. If you’ve got 20-odd players in your squad, you’ll work on two players not being available each week. If we can keep it to that, I’ll be delighted because it will give us a better chance.
“There are a lot of key issues in the second half of the season anyway, plus the fact you’ve got to get through this Christmas programme. Navigate that and if we’re still top of the league then we’ll be delighted.”