Mazzarri was axed on Friday to be replaced by Roberto Mancini.
"It was a difficult moment, because I really did not like making the decision to replace Coach Mazzarri," Thohir told the Corriere dello Sport.
"We believed in him because he is a hard worker and a good Coach, but this time more than my sensations I had to look at the numbers. Those were not good, because unfortunately the table speaks clearly.
"I have nothing to reproach Mazzarri for, as I know he gave his all every day and I thank him for that. However, all together we decided it was the right moment to change, that we needed a breath of fresh air for the whole environment."
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