Complex sentence: In 2002 he left Coventry to join FC Copenhagen, however, he suffered a serious knee injury 6 months after joining the club and never played football again; he announced his retirement in September 2003 due to this failure to recover from the injury.
Split into simpler sentences: In 2002 he left Coventry to join FC Copenhagen, however, he suffered a serious knee injury 6 months after joining the club and never played football again. He announced his retirement in September 2003 due to this failure to recover from the injury.