Grella, whose parents are Italian and therefore could play in Europe without work permit issues, lobbed the Barnsley keeper twice and later completed his hat trick with well-taken goal in the 86th minute.
Grella, a native of Glen Cove, N.Y., captured the ACC Player of the Year Award in 2008 after pacing the Blue Devil offense with 14 goals and eight assists for a career-best 36 points. He is a three-time All-ACC first-team selection and two-time All-American.
He was taken by New England in the third round of the MLS SuperDraft.
Leeds, a three-time English league champion, is a shadow of its former self. Beset by financial problems, the club languishes in the third level of English soccer. It's ninth in Football League One after 25 games.
Manager Simon Grayson used the game to showcase several players he hoped to unload before the January transfer window ends.
Scouts from other teams were on hand to watch the Leeds scrubs, so Grella's performance will have surely gotten the attention of other English clubs.