Van Gaal is yet to taste victory in a competitive game as United manager.
Keown told the Daily Mail: "If Van Gaal is determined to play with three at the back, he will be forced to leave out some of his creative players.
"You can't break the British transfer record and then not play Angel Di Maria, so Van Gaal will have to disappoint others. He won't drop Wayne Rooney or Robin van Persie so that means Juan Mata and Adnan Januzaj are left out.
"This still does not solve the problems in defence. Three at the back is such a difficult system to play and it clearly isn't working at the moment."
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