PSG have earmarked Doucoure as a prime target for the summer, which Mariappa believes is flattering for the Hornets.
"Look, we want to keep all our best players," said Mariappa. "It is a good thing to have players linked with moves, it means they are doing well.
"As a group, we are close and we pull together well. He is a big part of that, so we are delighted to keep him."