Mancini was confirmed as the man to take over from Mazzarri last week and will mark the start of his second stint with the club against rivals Milan on Sunday.
Having won Serie A and Coppa Italia titles during his first spell at San Siro, Mancini takes over with Inter ninth in the top flight and without a win in three matches in all competitions.
However, president Thohir claims he does not expect miracles, stating European qualification remains the objective as it was with Mazzarri.
"The objectives are the same as the ones we set Mazzarri: qualifying for Europe," he told Indonesian newspaper Topskor.
"The minimum goal is the Europa League, which now provides a route to the Champions League.
"I'm not asking for heroics, I will give Mancini as long as possible to build this team in order to achieve the ideal level of stability.
"The decision to hire Mancini went through thorough examination. I spoke with him, he's very ambitious."
