9. Ivan De La Pena
DAVE THOMPSON/AP/Press Association ImagesDe La Pena is now retired but he is a major what if in the club's history: what would we have achieved? If you were to hazard a guess, he'd probably have had a profound effect on the team. The creative midfielder started his career at Barcelona after coming through the ranks, and was touted as the young prodigy that would be the midfield successor to Pep Guardiola, and given the nickname "Pequeño Buddha" meaning "Little Buddha" due to his intelligent play and infamous lack of hair. He did enjoy a couple of short spells as a first team player, but was forced out to Italy to play for Lazio in a turbulent time for the talented De La Pena - he was even loaned back to Barcelona at one point, a testament to his ability - but this stuttering period caused the player to find himself in no-man's-land as a free agent. In 2003, Celtic came along: it wasn't so simple though, as Martin O'Neill couldn't trust that he was fit enough after his time out of the game. Celtic took him on trial for a week, but no signing was completed despite how much he impressed the management. Celtic then invited De la Pena back for another trial, but it was too late - De La Pena joined his old club's city rivals, Espanyol. The worst part of this is that De La Pena became one of Espanyol's most celebrated players, and lived up to the prodigal status of his youth.