United travel to Italy on Tuesday for the first leg of their last-16 tie and Mourinho expects a tight encounter.
The former Chelsea chief does not believe there will be much to choose between the sides until the very end of the second leg at Old Trafford but he is confident his men will ultimately progress to the quarter-finals.
"I have told the players that they have got to go into this tie and not be afraid of the possibility of, in 15 days, Inter being out of Champions League," said Mourinho.
"We have got to go into this tie thinking that in 15 days probably we can celebrate that we have beaten the European champions.
"Nothing will be decided tomorrow. After the game, we will all have the feeling that there is going to be another great game at Old Trafford.
"Probably come the last minute at Old Trafford, nobody knows who is going to go through.
"I am not expecting a result tomorrow that you can say it is done, that Manchester United or Inter have done it."
RespectMourinho has a good head-to-head record against Sir Alex Ferguson and he is relishing the prospect of pitting his wits against the Red Devils manager once again.
He explained: "From what I know of him as a coach, he has a lot of faith in himself and his team, and rightly too.
"If I am relaxed here now, he will certainly be the same, if not more relaxed than me.
"It will be a great pleasure to meet him again and it will be the same for him. We have had a great relationship from the start built on great respect and I hope it goes on like this to the end."
Inter have struggled to make much of a mark in the Champions League in recent years but Mourinho is not dwelling too much on history.
No blockHe said: "I don't think we have a block, I just think there are so many clubs in Europe who want to win the Champions League and not many of them can do it.
"This competition is different to the league where there are normally three or four teams who can win the competition.
"In the Champions League I think there are a minimum of 10 to 12 teams with the ambition, quality and capacity to do it.
"Inter in the past went out in the last 16 to teams like Valencia or Villarreal who they should normally be beating, but that's football.
"In 2004, Manchester United went out to a young Porto that nobody would have even bet a euro on winning and that's football."
Adriano and Zlatan Ibrahimovic are set to lead the Inter attack with Sulley Muntari, Esteban Cambiasso, Javier Zanetti and Dejan Stankovic in midfield.
Mourinho expects United to adapt their plans to combat Inter, adding: "I think Man United is of course a great team technically, but I watch with great attention every match in the previous season in the Champions League.
"Man Utd changed to play away from home. They are not going to come here to have fun.
"I am not saying they are afraid of us, no, but they respect us and they know that they can lose."