"Van Gaal's got a good track record but they need players," he told talkSPORT.
"He needs to bring four or five players in at least to get them back to where they were under Alex [Ferguson], where they were winning championships because they look well short of that at the moment.
"Certainly at this stage you wouldn't want to bet on them winning the league next year. I wouldn't see them winning it next year unless he suddenly pull three or four fantastic players out of the hat."
United finished in seventh place under David Moyes last season.