The Italian is not convinced that the opposition should have been awarded the penalty, which became the main incident of a mixed game at the Massimino.
Inter took the lead through Esteban Cambiasso, but a Sergio Almiron strike and a Francesco Lodi penalty turned the match on its head.
It was Gonzalo Bergessio who won the spot kick for Vincenzo Montella's men, but Castellazzi feels it is one of the softest he has seen given.
"I did not touch him [Bergessio]. In those circumstances the goalkeeper cannot just disappear, but he went down and he conned the referee," the goalkeeper told Inter Channel.
"There was no penalty. The penalty incident weighs upon us and the player dived for it."
Claudio Ranieri's men will have to pick themselves up for Tuesday's game against Lille in the Champions League.
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