The Premier League club have endured a very tough start to the Premier League season.
While they are still in relegation danger, Cunha believes O’Neil is a top coach who will get the team to safety.
“For me, he’s one of the best managers that I’ve had in my career," Cunha said, per Express and Star.
"He’s improved me a lot, not only as a player, but he’s improved me to be calm and manage situations. I can be frustrating and I feel like he can always help me in the every single point of being a human, a player and a man.
“I have a very good relationship with him and I'm so grateful with every single thing that we’ve built together.
"We are all a little bit said because we’ve not got the points we wanted and because we really want to give everything to the club and the results haven’t been coming, but we need to keep working.
“Gary is the kind of coach that it's easier to believe in because he shows you the things, and when the results will come back again, then the fans will believe a little bit more and more.
"I hope, as soon as possible, we will change it and keep showing everyone that we have very good staff, a very good group, and manage to go forward.”