Thohir bought control of Inter in October 2013 and saw them finish fifth in the Italian top flight last term.
The Indonesian businessman is confident coach Mazzarri has a good squad to pick from going forward, but admits there will need to be additions before 2014-15, especially in midfield.
"They (the squad) are well set, the positions of the players are correct, but that scores little and lacks speed on the counterattack," he wrote in Gazzetta dello Sport.
"We need to work on this, whilst it is not right to ask about objective without first knowing what the market will bring.
"Do we need new signings? We have a solid base. There is (Mauro) Icardi, who will grow, and (Rodrigo) Palacio in attack. Hernanes and (Mateo) Kovacic in midfield. (Samir) Handanovic, (Nemanja) Vidic, Juan Jesus in defence.
"The first thing we need is a strong defensive midfielder, one like Edgar Davids, like (Gennaro) Gattuso - to pressure, run, compete. In defence, it will depend on how we play, if with three or four."
Thohir has already begun the rebuilding work at Inter with the signing of Vidic from Manchester United, and the likes of Manchester City's Edin Dzeko and Chelsea's Fernando Torres have also been linked with a switch to San Siro.
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