Hughes worked with Dembele at Fulham.
"I've got huge regard for Mousa," the QPR manager said.
"He is an outstanding football player and now he is at a club which, and this is no disrespect to Fulham, has a higher profile and is getting a lot more attention.
"But he was still producing what people have seen in a short period of time, week in, week out for me and Martin Jol when I left.
"He is an outstanding footballer and I always knew when he came to the Premier League that he would make an immediate impact. He certainly has done that.
"He is technically very, very accomplished. He is able to play in a number of positions: he can play off the front, right up top, he can play in midfield, he can play in wide positions. That's the quality of the player that we are talking about.
"I knew almost immediately when he went to Tottenham that he would enjoy it and be able to fit in very, very quickly because he is an outstanding football player."