United are currently nine points behind Mourinho’s Blues side, with the defending champions a further two points adrift of leaders Arsenal.
Manchester United are Manchester United. Eleven points is quite a lot but I believe that they will push all the way
The 50-year-old Portuguese coach feels that the Gunners and Manchester City in particular currently have the advantage in the title race.
“No [I’m not writing United off],” Mourinho told his pre-match media conference.
“I think if you look at the table, obviously Arsenal and Manchester City are the top two teams.
“I repeat, City have different ammunition for such a different world for everyone. But we are not far.
“As I was saying, Liverpool have a fantastic chance to do it because its almost unique they’re not playing in European competitions.
“Manchester United are Manchester United. Eleven points is quite a lot but I believe that they will push all the way. For all the big teams, the big objective is to secure a top-four spot.”
Mourinho added that he views Sunday’s fixture as a special game and expects United to be strong despite their poor form under new boss David Moyes.
He continued: “I’m far too long in the game. I’ve played dozens of derbies, classic matches, matches between big teams, and this is what experience says.
“More than that, many times, the team that looks to be in the most difficult situation is the team that appears stronger in that match.
“That’s why I consider this game is special.”