Background: Juan Sebastian Veron (Spanish pronunciation: ['xwan sebas'tjam be'ron]; born 9 March 1975) is a retired Argentine footballer who as the chairman for Estudiantes de La Plata, where he had served as Director of Sports. A former midfielder, Veron's career started in Estudiantes, continued in Argentina's Boca Juniors, and included stints in several clubs in the Italian Serie A (where he won the Scudetto with Lazio and with Internazionale, and a UEFA Cup with Parma), and England's Manchester United and Chelsea. In 2006, Veron returned to Estudiantes, where he remained until his retirement in 2014, aside from a brief spell with Brandsen. He has announced his short return to first team will occur in Copa Libertadores 2017.
Context: After the 2000-01 season, he moved from Lazio to Manchester United on 12 July for a fee of PS24.3 million on a five-year deal, the most expensive transfer in English football at that time and becoming the first Non-UEFA player to break the English transfer record. On signing for Manchester United, he was quoted as saying that he had no fear of the Premiership. His spell at Old Trafford was not a great success. He had trouble adapting to the faster pace of the Premiership and was not allowed the same space and time on the ball. There was plenty of pressure on him at the start of his second season at Old Trafford and his performances did improve considerably, especially in the Champions League, where he excelled due to the slower tempo of the matches, scoring four goals, and was at the heart of United's successes in the group stages. However, injury meant that he missed much of the end of the season. Questions over his performance led to an expletive laden tirade against the media by manager Sir Alex Ferguson in support of Veron: "[Veron] is a fucking great player" were his parting words. "And you're all fucking idiots." However, fans and pundits alike agreed that the signing was an expensive flop. Veron later commented that the reason for his fitness problems and struggles with injuries at Manchester United were due to the less intense summer pre-season training in England. When Chelsea paid PS15 million for him two years on following the arrival of Roman Abramovich, Veron claimed that he wanted to stay and fight for his place at Old Trafford but Ferguson was willing to let Chelsea talk to him and he was eventually convinced by then Chelsea manager Claudio Ranieri that his future lay at Stamford Bridge, where he had much to prove. His transfer fee to Chelsea was about half that of his record-breaking transfer of just two years before. Veron made an excellent start to his Chelsea career by scoring the opening goal in a 2-1 victory over Liverpool at Anfield, but he fell away with injury problems as the 2003-04 season progressed and made only 15 appearances for Chelsea. The Times listed Veron's transfers to Manchester United and Chelsea among the 50 worst transfers ever in Premiership history. His several big-money transfers made Veron then the most expensive footballer in history with a cumulative total of PS77 million at that time. CANNOTANSWER
Question: When did he begin at Stamford Bridge?

Answer:

2003-04 season