Critics believe Pogba, who is currently recovering from injury in Dubai, has not performed well this season on purpose after missing out on a move to Real Madrid this past summer.
But Mata says the Frenchman has maintained a positive attitude throughout the season.
"Paul is genuinely a great guy," said the Spain international. "He's positive towards life and he's positive towards football.
"He's injured now but his attitude is good. As a midfielder, I've spoken many times about him, he's very complete as a player.
"For every club he would be very important, and for us he is very important."