Manchester United defender Lisandro Martinez has said he is constantly having to control his aggression towards his opponents in order to avoid picking up suspensions.

Martinez has impressed at Old Trafford since his summer move from Ajax, winning plaudits especially for his combative style.

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The 25-year-old puts his aggression down to his upbringing in Argentina and said it is something he is always trying to rein in.

"It is hard, it is really hard," Martinez said in an interview at United Carrington training base ahead of Sunday's Carabao Cup final against Newcastle United.

"Sometimes I want to kill but you have to control as well. I can do it otherwise I will be suspended every game. You have to be clever."

Martinez, alongside Raphael Varane at centre-back, has been key to United's resurgence under head coach Erik ten Hag this season.

He has recovered from a difficult start to life in the Premier League after defeats to Brighton and Brentford in August -- performances that prompted Sky Sports pundit Jamie Carragher to suggest 5ft 9in Martinez was too short to play as a central defender in England's top flight.

Carragher has since changed his mind but Martinez insists the criticism never bothered him anyway.

"To be honest, I put my full focus here, in the training. I can't control that, you know, it's just an opinion," Martinez said.

"I understand when people say that -- they show me who they are, you know? It's not my problem. I'm here, I'm really happy, the people are happy with me as well. That's the most important thing.

"I always train hard and, like I said, in an interview before, I don't have to show anything, I just have to show it here, with my people.

"For example, in the beginning, in Argentina, it was the same. But it's normal because, in football, it's not normal to play as a centre-back with my height. It's not easy as well, you know. I try to do my best, to be honest, but you have to work very hard. You have to be very clever on the pitch, because you have to be sharp in every situation, because if you're smart you can win the duels."

Martinez is set to line up alongside Varane at Wembley on Sunday as Ten Hag looks to win the first trophy of his United reign.

Victory would end a trophy drought of nearly six years following triumph in the Europa League under Jose Mourinho in 2017.

"We are very excited to play my first final here at Manchester United, and I think the team deserves it," Martinez said.

"For sure we're looking forward to it, and we want to win the final, for sure.

"Everybody knows how big Manchester United is around the world, it's one of the best clubs in the world and also I had been with Erik for three years at Ajax, I know him very well, so I think that was the key as well, to come here to Manchester United.

"I know him well, his mentality, we are almost the same in that way, for sure we want to win everything. That's why we are here as well -- we want to win trophies with Manchester United, we are working very hard, we're doing very well and are going in the right direction."