The 29-year-old has been a stand-out in the Premier League this season and has settled in well in his first season in England.
Roberts believes Wolves have unearthed a gem in Sa, but following a couple mistakes against Manchester City he feels the goalkeeper still has plenty to work on.
“We all know he’s done really well but I want to keep him at the level where he’s hungry and working more every day, which I try and do with all the goalkeepers,” Roberts said.
“We know he’s done well this season. He’s come in and you can see that from the stats.
“The club and staff know he’s doing well. We keep getting him to improve every day in training and in games.
“He’s learning from past experiences and has got that mentality to learn every day. He’s a character who is doing really well.
“There’s stuff he’s really good at and stuff he needs to work on, but he has the tools. He’s fast, athletic, powerful, has good size, is quick around the goal, wants to come for crosses and is mentally brave, as well as physically brave. He can save a shot, which is good, and he’s now getting better with his feet which is the modern trend.
“I’ve been happy with him. He’s still got a lot to improve. He still has potential to get even better.
“Week by week, game by game and hopefully the more seasons he gets here, he’ll get better and get to that level where Rui (Patricio) was, who was an institution here. I think we have a special one.”
Sa has been mentioned among the Premier League’s elite this season and for Roberts he tops the pile.
When asked where Sa ranks in the league, Roberts added: “He’s up there. I’ll be bias and say he’s the best in the league.
“He’s come in and from day one he’s had a winner’s mentality. He wants to win at everything.
“He wants to learn and look back at his training and games to learn from certain situations.
“If he’s caught a cross, where was his starting position and was he using the right technique. Or if he’s done something wrong, we break it down into small segments and try to practise it for next time, so he knows exactly what to do.
“I can’t give him enough praise. Of all the goalkeepers I’ve worked with over the years, he’s up there with one of the best.
“He has all the tools and is a bit mad. He wants to learn and if you want to be a top, top player these days you have to have that in you. We’re glad we have a load of players that want to learn. He’ll only get better.”