Greenhalgh, from Orpington, who played for Welling United youth team, was featured in the Sky One show Football's Next Star and impressed judges in the trial game after laying on a perfect cross for Hicham Abdellah to head home. At the end of the opening episode the judges had made their decision and presented the Inter Milan shirt to ten players who would now travel to Italy to compete for their dream of a professional contract in later episodes. After 20,000 entries to the show and 8 episodes Greenhalgh was given the shirt and revealed winner of Football's next star 2010 where he won a professional 6-month contract with Inter Milan.
After his 6-month professional contract at Inter Milan came to an end Greenhalgh was offered another year from the Italian giants which included a 4-month loan spell to Calcio Como where he scored 8 goals from 12 games. After his contract was up he returned to the UK and spent 4 months with Brighton and Hove Albion, as well as a spell at Birmingham City, where he was advised to play first team football in the Conference to gain experience in the English game. He signed for non-league club Welling United in December, before later joining Ebbsfleet United and Maidstone United. In June 2013 he transferred to Scottish club Inverness Caledonian Thistle. This was due to happen in February 2013 however international clearance stopped Greenhalgh leaving England until 13/14 season.