Long began his football career at Charlton Athletic in 1995 and progressed through the youth system at The Valley. He signed a three-year professional contract in 2002 after impressing manager Alan Curbishley. On signing the contract, Long said "signing a professional contract is what I have always wanted ever since I first came to the club and was playing for the Under-8 and Under-9 sides". Despite featuring regularly for the reserve team, Long was released in May 2005, ending his ten-year association with the London club. When released, Long said, "the club is in such a strong position now that it is difficult for young players to make the breakthrough".