Manchester City captain Vincent Kompany said the Premier League champions must take advantage of Manchester United's slow start.
Pep Guardiola's record-breaking City finished 19 points clear of United last season, while Jose Mourinho's side have lost two of their opening three matches this season.
"I'll give the neighbours a little bit, I'll have compassion for them, because Sir Alex Ferguson was such a big personality," Belgian defender Kompany said.
"You cannot take somebody like that out of a club and think that everything is going to continue like before. You always need a transition period.
"Manchester United are still dealing with a post-Ferguson era. So they will get that side of me, feeling compassionate. But any time it takes them to get back up, we need to take advantage of it."
City will play against Newcastle on Saturday, while United against Burnley on Sunday as they seek to avoid three consecutive defeats.