The Court of Arbitration for Sport began a four-day hearing in Lausanne on Monday which could result in three-times Tour de France champion Alberto Contador being stripped of his 2010 title for doping.
The 28 year old tested positive for clenbuterol last year and was initially cleared of any wrongdoing by the Spanish cycling federation, after he claimed he had eaten contaminated meat.
The International Cycling Union and the World Anti-Doping Agency both appealed, demanding that the rider should be banned.
Contador, who was accompanied by a team of elite sports lawyers faces losing his latest Tour de France title and a two-year ban from cycling
A verdict is expected in January.