<P> In July 2003, Gabriel Milito's transfer to Real Madrid from Independiente was cancelled after the medical examination by the Spanish club . Real Madrid doctors said Milito's knees would suffer severe injuries in the incoming years . Milito then signed with Real Zaragoza, becoming one of the most successful defenders in La Liga . In the incoming season, Zaragoza went to win the Copa del Rey final against Real Madrid . In 2007, he joined Real Madrid's lifetime rivals, Barcelona . </P> <P> In 2008, Lilian Thuram agreed to sign for Paris Saint - Germain on a free transfer from Barcelona . During his medical, it was discovered he had a severe heart defect which had also ended his brother's life, forcing Thuram to retire . </P> <P> In 2009, Milan were set to sign Aly Cissokho from Porto when a medical revealed he had a dental problem which could cause deterioration in posture and potential muscle problems, prompting Milan to cancel the transfer . Cissokho eventually transferred to Lyon one month later . </P> <P> On transfer deadline in January 2013, Nottingham Forest were attempting to sign George Boyd from Peterborough United when it collapsed due to an inconclusive eye test . Boyd later signed for Hull City in February, and subsequently scored against Forest in a fixture in March and mocked them with a celebration whereby he used his fingers to make fake glasses . A permanent transfer was arranged in May . </P>

How do transfers and loans work in soccer