The Naples club currently lie in 7th place in Serie A and chances of repeating their 3rd place finish in 2010-11 season look very slim.
Mazzarri has now told fans not to be disappointed if Napoli do not perform as well as they did last season. However, the Stadio San Paolo club are still competing in the Champions League.
"Last year we did exceptional things, but it is not always possible to repeat seasons like that one," Mazzarri told Sky Sport Italia.
"This term we are feeling more pressure after that splendid campaign and perhaps some players cannot handle it well.
"If Napoli are seventh in terms of budget and wage bill, then you cannot always expect something exceptional like last season."
Napoli will face Chelsea in the last 16 of the Champions League.