Complex sentence: In 2003-2004, under the guidance of Cesare Prandelli, who was renowned for his affinity for young players, Marchionni blossomed with 35 games played and 6 goals scored in Serie A and UEFA Cup.
Split into simpler sentences: In 2003-2004, under Cesare Prandelli, who was renowned for his affinity for young players, Marchionni blossomed under his guidance. That season has become a revelation in Marchionni's career with 35 games played and 6 goals scored in Serie A and UEFA Cup.