A father in France has been accused of drugging his children's tennis opponents, in what may be a case of obsessive determination.

Christophe Fauviau, a 45-year-old former military officer, testified in his trial on Friday about how their game collapsed after drinking courtside water.

Fauviau is accused of administering the anti-anxiety drug Tenesta to more than 20 players, one of whom died in a car crash induced by drowsiness.

"I began to feel unwell in the first set when I was leading four-three. I had vision problems and a loss of balance. I started seeing two balls," says a young man who could not be named because he was a minor at the time of his 2003 match against Fauviau's son, Maxime.