The highly-rated Nerazzurri goalkeeper had to be taken off at half-time in Bergamo on Tuesday but the coach has moved to calm long-term absence fears
The Slovenia international was forced off during the break after taking a heavy blow to his ribs during the first half of the game in Bergamo, with Juan Pablo Carrizo coming on his place.
Mazzarri, though, revealed afterwards that his first-choice keeper is unlikely to be out of action for too long.
"He received a heavy knock, as the doctor told me," the Nerazzurri boss told Sky Sport Italia. "But I do not think it's anything serious."
Mazzarri was more concerned by the state of the pitch at the Atleti Azzurri d'Italia, which proved treacherous for the balance of those playing.
"It's absurd to see Serie A players falling so much like this," the former Napoli boss fumed. "We even slipped in some important situations."
Mazzarri was also frustrated by his side's inability to hold on to a 1-0 advantage given to them by Ricky Alvarez, with German Denis having earned Atalanta a draw with a header.
"We have played well against a tough side," the 52-year-old mused. "It was brutal from a physical point of view.
"But if we're looking at the whole game, we did better; we could have won. But we were naive with the Denis goal. We must be more cynical when we're playing well."