Complex sentence: Dawson began his professional football career as a trainee at Leicester City in 2004 and although he became a regular in the reserve side, he did not graduated to the first team and rejected an offer of a new contract on reduced terms in May 2005.
Split into simpler sentences: Dawson began his professional football career as a trainee at Leicester City in 2004 and became a regular in the reserve side. He did not graduated to the first team and rejected an offer of a new contract in May 2005.