The former Holland manager has come under intense scrutiny this season as his side have played utterly dire football for the majority of the campaign so far, with fans and media united in showing their discontent at the lack of entertainment that has characterised United this season.
Parker, who played for United under Sir Alex Ferguson, was the latest in an ever growing list of former players to criticise Van Gaal’s tactical rigidity.
“I look at Anthony Martial and worry for him,” he wrote in his Eurosport column.
“He looks like a boy who doesn’t smile anymore. He doesn’t look like he’s enjoying himself.
“The form Memphis Depay is showing hasn’t just happened because he’s playing in the Premier League. That boy probably feels like a scapegoat. He’s in a country relatively close to where he’s from, but feeling a million miles away.”
Parker added that Van Gaal’s decision to leave Ander Herrera out of the side was puzzling, as the Spaniard has proved to be the kind of creative player United have been crying out for.
“Ander Herrera is hugely popular with the fans because he makes things happen. Everyone loves to see players like that, but he’s barely playing and is probably unsettled. These players need freedom they need to enjoy themselves,” he said.
“Looking further back, why did Angel Di Maria – arguably Real Madrid’s best player before he left them – start off great at United after a very good World Cup, then drop his performance by about 80 per cent? It was nothing to do with his house being broken into. You can deal with that.
“Van Gaal puts the fear of God into players. It has to be his way. He selfishly manages the team. And no one enjoys it.”