Grehan was born in
Glenrothes. After a spell in the
East Fife Youth system, Grehan spent some time in the Amateurs with
Fife side Kettle United. During his time at United he played with the Scotland Amateur Team. Grehan then joined
Scottish Premier League club
Motherwell from
junior team
Dundonald Bluebell in January 2008. He became the first junior player to join the club since legend
Dougie Arnott back in the late 1980s. 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 was released by Motherwell and then signed for
Scottish Second Division club
Stirling Albion in the summer of 2008. Grehan was unveiled by manager
Ian McCall on 29 January 2010 as a
Partick Thistle player having signed for an undisclosed fee. He scored his first Thistle goal to give
The Jags a 2–1 victory, away to
Ross County, during the second last match of the 2009–10 season. After his spell at Thistle, Grehan moved to
Stranraer. 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. Grehan signed for
Alloa Athletic in the 2012 summer transfer window. However, after only one season at Alloa, he was released by
Paul Hartley in May 2013. Grehan then returned to
Stranraer for the
2013–14 season in June 2013. Grehan departed Stranraer after one season and signed for
League One rivals
Stenhousemuir on 6 June 2014. Grehan had a short spell with
Arbroath in 2015, before dropping back into junior football with
Kilbirnie Ladeside in February 2016. Grehan signed with
BSC Glasgow in 2017 and spent three seasons with the
Lowland League club before announcing his intentions to move on in July 2020. On 5 October 2020, Grehan signed for
West of Scotland League team
Gartcairn. He later resigned with BSC Glasgow on 7 January 2021.
Drumchapel United announced the signing of Grehan on 22 May 2021. ==References==