Jones limped off during the second half of England's 2-0 win in their Euro 2016 qualifier in Switzerland on Monday and he is now likely to be out of action for at least four weeks.
"Phil has a torn hamstring," Van Gaal said
"He is maybe out for three weeks or a month."
If Jones is out for a month he will miss United's next four games and his place in the England squad for October's double-header against San Marino and Estonia will also be in doubt.
Dutch boss van Gaal is still searching for his first competitive win as United manager ahead of Sunday's Premier League match at home to Queens Park Rangers.
Source : AFP
Source: AFP