Prolific as an amateur and winning the 5 a-side Scottish Cup 2003 in Dunfermline and 2004 edition in Hamilton with Inter Silky Soccer.
Grehan then joined Scottish Premier League club Motherwell from junior team Dundonald Bluebell in January 2008.
[1] Soon after, Grehan went on a month's loan to Scottish Third Division club Forfar Athletic, and made an immediate impact by scoring on his debut.
Grehan went on to play 27 games for Stranraer, scoring 5 goals, as the club reached the end of season play-offs, losing in the final against Albion Rovers.
[12] Grehan signed with BSC Glasgow in 2017[13] and spent three seasons with the Lowland League club before announcing his intentions to move on in July 2020.