move. During the January 2006 transfer window, Rangers made a £400,000 bid for Riordan that was rejected by Hibs. Bids from Lokomotiv Moscow and Kaiserslautern were accepted by Hibs, but Riordan rejected these moves because he did not want to move overseas. Riordan caused controversy in 2005 when he appeared in a video that showed him singing that Hearts player Rudi Skácel was a "fuckin' refugee", to the tune of The Beatles's "Yellow Submarine". Riordan later apologised for his actions. Celtic Riordan signed for Celtic in a £170,000 deal in June 2006. The fee was reduced from the previous offers because Riordan's contract with Hibs was due to expire in October 2006, and Riordan had already made a pre-contract agreement to sign for Celtic on a free transfer in January 2007. Riordan made his full debut for Celtic in a Scottish League Cup tie against St Mirren, as Gordon Strachan fielded a team containing many players who were not first team regulars. He had difficulty obtaining a regular place in the Celtic team; he made only 24 league appearances in two seasons with the club. Riordan publicly aired his disappointment at not being given more opportunities in the Celtic first team in April 2008, and he subsequently trained with the reserve team. Burnley made a £400,000 offer for Riordan in January 2008, but this was rejected by Celtic. Five other clubs, including his former club Hibernian, made loan offers for Riordan, but Celtic rejected these and informed Riordan that he would have to leave on a "permanent" deal. Hibernian made another loan offer to Celtic for Riordan in August 2008, but this was also rejected by Celtic. Return to Hibernian Riordan returned to Hibernian on the final day of the 2008 summer transfer window for an "undisclosed" fee believed to be around £400,000. Hibs initially gave Riordan the unusual squad number 01, as number 10 had already been allocated to Colin Nish. Riordan was given the number 10 shirt for the 2009–10 season; he was able to do this as Nish had taken number 9 after Steven Fletcher left the club to join Burnley in the summer of 2009. Riordan made his second debut for Hibernian on 13 September 2008, when he came on as a 61st-minute substitute for Joe Keenan against Dundee United. In his second appearance, he scored the only goal of the match against Hamilton Academical. Riordan