Deulofeu has missed much of the second-half of this term after knee surgery.
“It's really tough because I know my teammates are going to miss me because I'm doing really good things for the team," he said.
“But there are more players who are going to take this opportunity. We have great players who are going to help the team and we're going to achieve our objectives to remain [in the league] of course.
“He's [Sarr] a really good player, really young, his pace is amazing and it helps the team a lot because when we do the counter-attacks from both sides – from my side and Ismaïla's – the team can go up [the pitch] and it helps the team a lot.
“He gets good assists, good goals. In the present and in the future, he's going to be a really good player for Watford so we're really happy to have him in the team."