Mata and Herrera reportedly feel stifled by van Gaal's tactics.
Reports have suggested that Gabriel Agbonlahor and Charles N’Zogbia have not responded well to Remi Garde's appointment at Aston Villa.
The Nottingham Forest striker gave little away.
Sunderland face tough assignments against Manchester City and Liverpool before 2015 concludes.
Sheffield Wednesday host Birmingham City on Boxing Day.
The Leeds boss admits they may need to sell the talent this winter.
The Saints are on a miserable run while Arsenal have recently been installed as the bookies' favourites for the Premier League title
The Brazilian believes that the Reds are in a great position to be lifting silverware this term.
Paul Merson has hailed West Ham playmaker Dimitri Payet.
The Gunners beat Manchester City on Monday evening to go two points from first placed Leicester City.