Cilic's Return Raises Questions About Antidoping Protocols PARIS - Marin Cilic lost to Juan Martín del Potro in the second round of the ATP Masters event in Paris on Wednesday, but his overall feeling was one of relief. Cilic, a former top-10 player from Croatia, was happy to be in action after being among the highest-ranked tennis players to serve a doping suspension. He compared his sensations on court to "a kid playing for the first time," and said his positive test caused "the worst time of my life." In early May, Cilic tested positive for the prohibited substance nikethamide, an ingredient in glucose tablets he had taken. Cilic began taking glucose powder in 2011 to aid in the digestion and absorption of creatine powder, a permitted supplement that boosts energy levels. But when his supply of glucose powder ran low at a tournament in Monte Carlo in April, he asked his mother to buy him some more at a pharmacy. She bought a different form of glucose than he normally used, he said, and the tablets, with warning labels written in French, contained the banned substance nikethamide. In September he received a nine-month suspension from the International Tennis Federation, which said it believed Cilic did not attempt to use nikethamide as an illicit performance enhancer. Cilic appealed to the Court of Arbitration for Sport, which last week reduced his suspension to four months. Cilic, now ranked 41st, had already served four months since accepting a voluntary suspension in June, so he was able to make an immediate comeback this week. Although the arbitration court has not yet released its full decision, Cilic suggested that much of the court's ruling in his favor hinged on technical points about the specific substance for which he tested positive. Cilic said he tested positive for a metabolite of nikethamide called nicotinamide, not for the stimulant nikethamide itself. Additionally, nikethamide itself is only a banned substance in competition. It is legal out of competition, so finding a lingering metabolite of it would not necessarily indicate that he had taken it illegally during competition. What drew attention to Cilic's ban was not the technicalities on which it ended, but the manner in which it began, with him quietly withdrawing from Wimbledon under the veil of a knee injury. In the early afternoon of the third day of Wimbledon, Cilic, the No. 10 seed in the men's singles draw, inconspicuously withdrew before his second-round match, citing a left knee injury. At a news conference on the day of his withdrawal, Cilic spoke about the trouble he had putting weight on his left leg, saying that his knee had bothered him for a "couple weeks." Cilic's withdrawal was hardly dwelt upon at the time. It was only part of an exodus on the third day of the tournament that included Roger Federer, Victoria Azarenka, Jo-Wilfried Tsonga and Maria Sharapova. The 10th-seeded Cilic, who called it a "very black day," had no explanation for the sudden cluster of falling stars. "Everything is related to individual," he said. Difficult to say what the real issue is. As it turned out, it was difficult to know what Cilic's own "real issue" was. About a month after Wimbledon, the Croatian news media reported that Cilic had withdrawn from Wimbledon after accepting a voluntary provisional ban. The tennis federation does not comment on doping cases that have not been ruled on by an independent tribunal, so Cilic spent the next several weeks pulling out of events, including the United States Open, citing personal reasons. When the federation's independent tribunal handed down its ban in September, the report said that Cilic had withdrawn from Wimbledon citing "a knee injury to avoid adverse publicity." Cilic denied that his knee injury had been feigned and emphasized that a deciding factor in accepting the voluntary suspension was that his results at Wimbledon might have been invalidated later. Stuart Miller, the federation's antidoping manager, applauded Cilic's willingness to remove himself from competition. "Voluntary suspension, I think, is a good thing for a player to do because it does demonstrate a good attitude toward the integrity of the game," Miller said. Miller said that in his seven years leading the federation's antidoping system, players had rarely chosen to begin a voluntary suspension in the middle of a tournament. He added that it was not the federation's responsibility to ensure the accuracy of any explanation given for suddenly pulling out of a tournament.