Lucas Arnold Ker

Lucas Arnold Ker (; born 12 October 1974) is a retired professional tennis player from Argentina.
Arnold Ker started playing tennis in the Olivos Tenis Club of Buenos Aires, under coach Malcolm Campbell. He is the younger brother of Patricio Arnold.
He is right-handed and turned professional in 1994. He has played several times for the Argentine Davis Cup team, where he made his debut in 1997 against Venezuela. He was Roger Federer's opponent in the Swiss' first professional match in 1998, beating the 17-year-old future great in straight sets.
Cancer.
In August 2006, he was diagnosed with testicular cancer. The testicle was removed, and he successfully underwent chemotherapy. In 2008, he was in remission and returned to playing professional tennis.