Cristiano Ronaldo intends to "close the mouths" of those who have questioned his defensive work by firing Manchester United to silverware this season.

The Portugal international has made a huge impact in an attacking sense since returning to Old Trafford from Juventus in a shock transfer two months ago.

He has scored a team-high six goals in eight appearances, including late winners in the Champions League victories over Villarreal and Atalanta.

However, with United struggling for consistency in the Premier League ahead of Sunday's clash with Liverpool, Ronaldo has been criticized by some for his lack of defensive effort.

Indeed, Opta data shows only defenders Raphael Varane, Harry Maguire and Victor Lindelof are averaging fewer pressures than Ronaldo (12.1) for United in the league this term.

But Ronaldo has hit back at his critics by pointing out his past glories, which includes a haul of 31 trophies for club and country since his first spell with United started in 2003.

"I know when the team needs my help defensively. But my role is to win, help the team to win and to score goals – [the defensive side] is part of my job," he told Sky Sports.

"The people who don't want to see that is because they don't like me. But to be honest I'm 36, I win everything so am I going to be worried about the people who say bad things about me? 

"I sleep good at night. I go to my bed with my conscience very good. Keep going with that because I will still close mouths and win things.

"Criticism is always part of the business. I'm not worried about that. And I see it as a good thing, to be honest. 

"If they worry about me or they speak about me, it's because they know my potential and value in football still. So it's good.

"I'll give you an example: if you're in a school and you're the best student, you ask the worst student if he likes the best, they'll say they don't like him."

United rank eighth in the English top-flight for high turnovers as a team this season with 66, compared to 87 for the next opponents Liverpool.

Ronaldo has every right to feel confident in his goalscoring ability, though, having become the first player ever to finish top scorer in Serie A, LaLiga and the Premier League with his 29 league goals for Juventus last season. 

And while he may be approaching his 37th birthday, Ronaldo insists he has no current plans to call time on his illustrious career.

"I think the main word is that I'm still happy and enjoying football," he said. "It doesn't matter how many things I won in my career. I win everything but I'm still motivated. 

"I'm in a new chapter of my life, even with my age, and this is why I am here –  to try to win and I think Manchester needs to be at this level of winning and thinking to win big things so I'm here to help."

Ronaldo is expected to start when United welcome fierce rivals Liverpool to Old Trafford on Sunday.

United trail their opponents by four points and have won just one of their last 10 Premier League meetings with the Reds, losing this exact fixture 4-2 last season.