Argentinian Pereyra, 28, has been one of the Hornets standout players this season.
Sergio Furlan said: “2018 was the year of his take-off. He scored a dozen goals in a calendar year, something he'd never done before, and we're talking about a midfielder, not a striker.
“He starts from the left and comes inside. The coach [Javi Gracia] is getting the best out of him in this position and he's doing very well.
“Mazzarri likes him, but so does Sarri. Maxi has great esteem for Mazzarri because he's a sincere man."
Furlan all but ruled out a January move for Pereyra but admitted the Watford star has his sights set on a return to European football.
He added: “A transfer in January? You can never say never in the market, but I tend to exclude it almost categorically.