United meet Sevilla this week in the first-leg of their round of 16 clash.
Mourinho said: “In the last 16 I don't speak about contenders. Only those couple of teams who season after season are always there, always in the finals.
“I think at this moment we are just one of the 16. The next round of the Champions League is the one that I consider really fundamental.
“It is the one that makes you go from 16 to eight and when you are in the last eight then yes, you become a contender even if you are not the favourites.
“That's always the way I felt in my previous Champions league. When you're in the 16, 16 is too much.
“But after two matches and you become eight then you have the draws and you sometimes have combinations that may open some door a little bit more.
"But now I think it's too early to say any more."