United striker Mark Viduka made a hefty challenge inside the first five minutes while Jody Morris caught Glen Little with a late tackle.
Burnley skipper Paul Weller reacted angrily to the challenge by pushing Morris to the floor and punches were traded between players of both sides in what developed into an ugly clash.
Burnley boss Stan Ternent even took the unusual step of entering the field to calm things down.
Both Ternent and Peter Reid refused to comment on the brawl, but the managers were thought to be more than happy at the common sense approach adopted by Leake.
However, new FIFA directives state that referees must treat friendly matches in the same manner as competitive games and Leake could now join Kaye in being hauled up before the FA.