Gregory was a part of the U19 squad at UCD before being named in the first team by Aaron Callaghan for the 2014 Premier Division. He made 4 league appearances towards the end of the season as UCD were relegated from the Premier Division after losing to Galway FC in the play-offs.

Injury restricted Greg's contribution in 2015 and he made just five league appearances for UCD who lost out in the promotion play-offs to Finn Harps. But in 2016 he became a fixture in the Student's midfield, scoring four times in 22 league appearances as UCD finished fourth in the First Division table.