The BBC in London was one of several media outlets reporting Sunday blood tests did not turn up any proof of his allegation.
The tests, conducted in New York by the International Tennis Federation, occurred after Haas' teammate, Alexander Waske, claimed a Russian team manager told him in Moscow Haas had been poisoned.
"He said as an aside it was a shame that Tommy had been poisoned," Waske told The Times of London this month.
The German Tennis Federation Web site quoted Haas as saying: "It's no longer an issue. The tests gave no results (and) it was too far in the past."
The day Haas fell ill, he was beaten in straight sets, and eventually, Germany lost 3-2 after dropping both matches on the event's final day.
He was unable to play in the reverse singles because of gastro-enteritis.