Barnsley boss Paul Heckingbottom says Fletcher will target a first team role at Old Trafford.
De Gea's deadline day move to Real Madrid collapsed last September.
Van Gaal believes the club are still in a period of transition.
The 28-year-old Belgian could face an FA ban after an elbow on Leicester City defender Robert Huth.
Red Devils scouts have been watching French forward in action in Spain, according to reports.
The 53-year-old Portuguese has been linked with the Old Trafford club since he was sacked by Chelsea.
Victor Valdes helped Standard Liege beat Club Brugge to win the Belgian Cup in March.
Luke Shaw has been sidelined since September last year after sustaining a double leg fracture.
Shaw is progressing 'very well' as he steps up return bid after seven months out with a double leg fracture.
Leicester City are one win away from lifting the Premier League this season.
Manchester United will be keen to deny Leicester City the chance to wrap up the Premier League title at Old Trafford on Sunday (1 May).
Tahith Chong has been on Manchester United's radar for over a year after impressing in a youth tournament in 2014.
Louis van Gaal has one year left on his contract at Manchester United.
Robert Lewandowski has been prolific for Bayern Munich this season scoring 38 goals in all competitions.
Marouane Fellaini has started just 11 Premier League games this season which could prompt a summer move.
Despite voicing approval, the 62-year-old pundit does not see the Portuguese coach replacing Louis van Gaal.
Wayne Rooney says he knew years ago that he has to move to midfield.
The star reportedly earns £140k a week at Old Trafford but insisted he hates the business aspect of the sport.
Louis van Gaal will be reportedly allowed to step down from his post after the end of the 2015/16 season.
Arsenal suffered back-to-back defeats at the hands of Manchester United and Swansea City in the Premier League.
Manchester United face Everton in the semi-finals of the FA Cup as they battle City and Arsenal for a place in the top four.
The Foxes are currently five points ahead of second-placed Spurs in the Premier League table.