Complex sentence: He would be "upgraded" definitely in the following season, but would never be an undisputed starter; on 20 December 2003, he scored a late penalty in a 2--2 draw at Atlético de Madrid.
Split into simpler sentences: He would be "upgraded" definitely in the following season, but would never be an undisputed starter. On 20 December 2003, he scored a late penalty in a 2--2 draw at Atlético de Madrid.