Guarin is expected to leave Inter next week.
Mazzarri said: "I don't want to talk about the transfer market, especially today. It's an issue to discuss with the club regarding financial fair play and balancing the books, but a Coach can only really take heed of the decisions made by his club.
"The way I see it, Guarin responded on the field. I had many individual meetings with him, as in my view he hasn't expressed over 90 minutes his full potential. I called him on Tuesday and said he'd played the best game against Napoli, showing that consistency I wanted. Perhaps these rumours stimulated him to give his best."
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