United are without the suspended Nemanja Vidic and fellow centre back Jonny Evans is struggling with an ankle knock but Mourinho still thinks Alex Ferguson will try to play it tight.
"I don't believe Manchester will come to the San Siro to win, they will play very defensively," Mourinho told a news conference on Monday.
"I am sure that tomorrow nothing will be decided but everything will come down to the return leg at Old Trafford (on March 11)."
The game brings the charismatic Portuguese face to face with Ferguson for the first time since he left Chelsea in 2007, having beaten United to the English title in 2005 and 2006.
Mourinho, whose Porto side knocked United out on their way to winning the Champions League in 2004, has got the better of Ferguson most of the time -- winning six, drawing five and losing one of their 12 meetings.
Inter have only won the European Cup in 1964 and 1965 but Mourinho was keen to take the pressure off his players.
"They don't need to be scared, we must always keep our individuality," he said.
"To eliminate Manchester would be nothing special, the important thing is to reach the next round. We have no fear, I think we will be in the final in a few months."
Despite stumbling through the group stages, Inter are nine points clear in Serie A and Mourinho sees no reason to change his tactics against the in-form Premier League leaders.
"We will not change our way of playing. It will be 4-4-2 with a diamond midfield. (Zlatan) Ibrahimovic and Adriano will be in attack," Mourinho said.
The Portuguese, who succeeded Roberto Mancini as coach in June, started the season trying to recreate the three-man attack that worked for him at Chelsea but quickly abandoned the idea.
Inter have since relied on their physical power and aerial ability in the box to bludgeon the rest of Serie A.
Centre back Walter Samuel is almost certainly out with a calf strain.
