Cesar, capped 64 times by his country, joined the R's from Inter Milan this summer and has made a seamless transition to English football.
And Hughes, while hailing Cesar's attitude both on and off the pitch, says the 33-year-old is up there with the goalkeeping greats.
"He's been an absolutely remarkable signing for us," Hughes told the club's official website.
"Not only his ability as a keeper, but as a guy. His mentality in the dressing room is huge for us. And that's a real benefit we'll tap in to.
"He understands what it takes, he drives people around him and inspires people by his manner and presence.
"Over the years I had the pleasure of playing with (Peter) Schmeichel and (Neville) Southall and he's right up there," he said.
"I haven't seen Julio over the time I've seen Schmeichel and Southall, but I've been very much impressed with what I've seen.
"He's very much on a par with the top keepers in the world in my view."