In the biggest game on the Italian football calendar, Inter and Milan will face each other at San Siro this weekend.
Walter Mazzarri's men made a promising start to the season but have not won any of their last four league games, leaving them fifth in Serie A.
They are still five places and nine points above their city rivals, and Indonesian businessman Thohir, who now owns 70 per cent of Inter, is confident of a good result.
"I'm not worried by the team's results," Thohir said.
"I trust the players. I think they're giving their best. I also think the game between us and Napoli (Inter lost 4-2) was a good game.
"This is one of the most important games of the year. I can't wait for it to arrive. I'm going to be at the stadium and certainly it would be beautiful to win it, but we mustn't underestimate Milan because they also have a good side.
"I hope our coach and team arrive at the game well prepared. I know it won't be easy, but we've got to give it our best.
"Italian football is not easy, but I do think we're preparing well for the derby."
Inter goalkeeper Samir Handanovic has urged his team-mates to turn their form around for their clash against Milan.
"We were doing well for the first five or six games, but we've taken a step back lately," Handanovic told Gazzetta dello Sport.
"We need more hunger, more aggression."
