The centre-back has been one of the club’s better players since turning their form around in recent weeks, however hasn’t been free of criticism and came under scrutiny following the Red Devils’ defeat to Real Sociedad in the Europa League on Thursday.
Speaking to Bet365, Stam said: “Defensively, he’s very aggressive, sometimes he needs to be a little bit more aware of his opposition, not get caught or be too aggressive.
Martinez struggled in the opening weeks of the season as United suffered defeats to Brighton & Hove Albion and Brentford, but has since looked comfortable at the heart of defence alongside Raphael Varane.
Despite another difficult result in the Europa League, Stam still had plenty of praise for the 24-year-old.
He added, “He’s a good player. I knew as soon as he arrived people in the UK would talk about his height. That can be an issue as a centre-back, not being so tall, but he’s shown his quality over here in the national team and in the Champions League.
“As a player he’s very comfortable on the ball. You can see he’s trying to find these passes in between lines.”
Despite his glowing reports from his time in the Netherlands and his £56.7 million price tag, his 5 ft 9 frame has been the most discussed topic since his arrival in the Premier League.
However, the Argentina international has quickly displaced Harry Maguire and Victor Lindelof in the starting line-up.