Manchester United have defeated Burnley 3-1 in a practice match behind closed doors at Old Trafford, with Anthony Martial, Jesse Lingard and Fred on the scoreboard.The match against the Clarets was arranged to help build fitness and give some United players a chance to get some playing time before the Premier League season continues this weekend with a trip to the south coast to face Southampton.Jadon Sancho, who made his United debut from the bench during Saturday's 5-1 win over Leeds, started the match to build up his…