The Ligue 1 outfit arrive at San Siro with a 1-0 advantage from last month's first leg meeting at the Stade Velodrome.
However, Deschamps believes that Marseille remain clear underdogs to progress to the quarter-finals and feels that all of the pressure is on their hosts.
"Our first leg success certainly gave us a little advantage but Inter are the favourites," the former France international told reports on the eve of the game at the Giuseppe Meazza.
"We have nothing to lose. Inter are a great team and they will do anything to get through.
"Tactically, it will be very important to defend but also to score and perform well. This is our aim.
"Inter can only win but we can also draw. Our aim was to reach the knockout phase but we will do our best to keep going as far possible."
Marseille go into the game on the back of four successive defeats in the French championship, but goalkeeper Steve Mandanda does not believe that their dismal domestic form will affect their performance in Milan.
"It's clear that we just lost four straight games, so we do not arrive here in the best shape," he conceded.
"But this is a different competition. We know there is a place in the quarterfinals at stake at the end of this match.
"It will be difficult, against a good team. But I think we're in the right frame of mind because the first leg went well for us."
Marseille's meeting with Inter at San Siro gets underway at 19.45.
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