Inter expects to progress to quarters
Despite the backing of Inter president Massimo Moratti, Ranieri's position has become uncertain following a poor run of results.
Milito scored in added time to seal the win and the Argentinian believes the overdue success will inspire them to turnaround the deficit against an OM side who are themselves struggling.
"We're convinced we can overturn the result. We played very well in the first leg and didn't deserve to lose," he said.
"We're sure that we can win with the help of our fans.
"We're sure we can still do well in the Champions League. Of course it is a different sort of competition. If we get through this round we'll be among the top eight teams in Europe.
"Tuesday's match is massive and we're desperate to do well. And after that we'll have everything to play for - this team have already shown they're capable of going all the way."
Moratti offered Ranieri his full backing after the win at Chievo, although an early Champions League exit could test his patience.
"It's not easy for a coach to read in the papers every day that there's a new coach coming in to replace him," Moratti told Sky Sports Italia.
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"Ranieri is professional, he's getting on with his job and he has my complete support in this difficult time that he's experiencing and that we're trying to get through."
Despite Ranieri's problems his opposite number, Didier Deschamps, is under just as much pressure following an alarming slump in form.
Since beating Inter, OM have lost their past four league games, without scoring, to slip to eighth in the Ligue 1 table.
A 1-0 reverse at relegation-threatened Ajaccio at the weekend was only sweetened by the return of star striker Loic Remy from injury as a half-time substitute.
The France international is set to start at San Siro on Tuesday night and fellow attacker Mathieu Valbuena believes he could help claim a win to turn their season around.
"If we are fortunate enough to qualify for the quarter-finals, it will give us the confidence and serenity for the rest of the season," he told L'Equipe.
"Our recent results have not been good. If we can get through this it will be huge."