The £30 million summer signing will not be able to make his debut against Swansea City, leaving the Red Devils short of a natural left-back for the start of the season
The 19-year-old joined the club from Southampton for £30 million this summer after playing his way into the PFA Premier League Team of the Season in 2013-14 but will have to wait for his debut.
It leaves United short of a full-time left-back for the start of the Premier League season, though Ashley Young has played on the left of a 3-5-2 at times in pre-season and could feature in that position against Swansea City.
Van Gaal had declared after his arrival at Old Trafford that the England international, who went to the World Cup earlier this year, was out of shape.
Goal understands that United are pressing ahead with plans to sign Daley Blind and are also targeting Sporting Lisbon's Marcos Rojo, both of whom would be comfortable in Shaw's position.
Shaw has just been handed the No.3 shirt by Louis van Gaal, having succeeded both Patrice Evra and Alexander Buttner in his position this summer.