Viktor Troicki's doping ban for skipping a blood test was reduced from 18 months to 12 on Tuesday, though the Serbian tennis player still cannot play in next week's Davis Cup final.
The Court of Arbitration for Sport ruling "puts an end to my dreams of being a top player," the 27-year-old Troicki said in a statement.
"I worked my entire life for it, and it has been taken away from me in one afternoon by a doctor I didn't know," he said.
Troicki's ranking peaked at No. 12 in June 2011. It fell from No. 53 to No. 77 since he was suspended by the International Tennis Federation in July. In 2010, Troicki won the decisive singles in the final against France to give Serbia its first title.
Troicki's appeal was partially upheld. The top court in international sports ordered him to serve a 12-month ban for missing a blood test after losing at the Monte Carlo Masters in April.
He blamed a tournament anti-doping officer who he contended advised him to write to the ITF explaining that he was ill and could not give a blood sample. He had already given a urine sample that later tested negative.
"The player committed a doping offense, but his fault was not significant," the court said in a statement.
Troicki will be cleared to play again July 15, having missed four Grand Slam events while suspended.
"I have no idea about what to do now or where to go. I hope somehow I will be able to fight back," he said.
Serbia plays the Czech Republic in the Davis Cup final in Belgrade next week. Troicki appeared in the first two rounds this year. The international court fast-tracked Troicki's case to give him the chance of reselection if his appeal had been successful.
Troicki's home federation described the verdict as "humiliating and disappointing." It added in a statement that Troicki has been "inflicted a major injustice."
ITF President Francesco Ricci Bitti said rules had to be applied strictly "to keep our sport clean."
"What is harder to accept is criticism of doping control officers who perform a difficult role," Ricci Bitti said in a statement.
Top-ranked Rafael Nadal expressed support for Troicki, whom he called "a good guy."
"I hope to see him back on tour next year," Nadal said at the ATP World Tour Finals in London. "The doctor who accepted to make the control the next day, if that's that way, that's a big mistake from the doctor, too."
The CAS panel acknowledged that the tournament anti-doping officer "should have informed the player in clearer terms of the risks caused by his refusal to undergo a blood test."
The court added "there was no suggestion that Mr. Troicki intended to evade the detection of a banned substance in his system."
The three-member CAS panel said that Troicki and the doping official, a Ukrainian doctor, gave their evidence in good faith in Lausanne one month ago.
However, the panel's ruling published by the ITF noted that "the recollection of the athlete in particular was colored by his subsequent reconstruction of events."
A one-year ban was considered a "just and appropriate sanction" by the panel, and the minimum required in such a case according to ITF anti-doping rules.
The ITF tribunal in July declined to impose the standard two-year ban for a first anti-doping violation because it accepted Troicki was stressed by illness on the day and his long-standing needle phobia.
The ITF said Troicki remains disqualified from the Monte Carlo Masters, but retains his prize money and ranking points from subsequent events, including his run to a fourth-round loss against Jo-Wilfried Tsonga at the French Open.
AP Sports Writer Samuel Petrequin in London and Associated Press writer Jovana Gec in Belgrade, Serbia, contributed to this report