Although admitting that his side's recent 2-0 loss to Chelsea was disappointing, the 51-year-old coach remained adamant that a sense of positivity is present in the dressing room and hailed the work ethic of his troops.
"I had a meeting with the lads earlier to show them that apart from some of the mistakes we made and must try not to repeat, we did good things and played good football against a top-notch side," Mazzarri told his club's official website.
"The lads have a greater awareness of what we're doing now and for a coach that's very reassuring to see."
"I showed them that we played some decent football, that we created four or five chances. It's all looking very good.
"Analysing things calmly I can say that having coached this team for a very short period I've already seen things that go way beyond even the best hopes I had."
Mazzarri then turned his attentions to the upcoming match, recognising the quality which opponents Valencia posed.
"They are difficult to play against because Spanish teams don't give you any reference points and Valencia are a very well-drilled side," the former Napoli boss mused.
"It's going to be an important test for when we go into games needing to be properly prepared, when there are points to be won.
"So it's a useful opportunity for us to correct some of the defects we might still be showing."
Mazzarri succeeded Andrea Stramaccioni at the helm of the Nerazzurri earlier this summer, after parting company with Napoli following four successful seasons at the San Paolo.