Marin Cilic's announcement during Wimbledon that he was pulling out of the tournament due to a knee injury was to avoid "adverse publicity" from the fact he had failed a drugs test, the full findings of the case have revealed.

The Croatian, who was No10 seed at the All England Club this summer, was banned for nine months last week after testing positive for a banned supplement.

He had been one of the leading players at Wimbledon, having finished runner-up to Andy Murray at Queen's, but pulled out of his match against France's Kenny de Schepper on 26 June having accepted a provisional suspension for the positive test – but cited a knee injury as the reason. He was one of seven players to withdraw – such a higher number led to an inquest into the state of the courts.

The findings by the International Tennis Federation's independent anti-doping tribunal stated: "He [Cilic] played and won his first-round match at Wimbledon on 24 June. He has not played in a competitive match since.

"On 26 June his lawyers in Brussels responded on his behalf, voluntarily accepting a provisional suspension until a decision in the case, and waiving his right to analysis of the B sample. He withdrew from Wimbledon, citing a knee injury to avoid adverse publicity."

Cilic, 24, tested positive for the banned supplement nikethamide after taking Coramine glucose tablets bought at a pharmacy in Monte Carlo. The tribunal heard the tablets' information leaflet contained a warning for athletes that they could lead to a positive test, but Cilic argued that he could not understand French.

The tribunal's findings stated that the player could easily have checked before taking the tablets, but accepted he had inadvertently ingested the nikethamide and "did not intend to enhance his performance in doing so".

They added: "The product had the word 'Coramine' in upper case letters on the front. The player was familiar with websites such as Google and Wikipedia. It would have taken only minutes to search under 'Coramine' on those sites, and discover the danger he was in."

Cilic had also stated that he was under considerable stress due to problems between his coach Bob Brett and his parents. The tribunal accepted that but said: "We do not, however, think that the stress the player was suffering is a factor of great weight. Conditions in the highest echelons of professional sport are inherently stressful."

The tribunal said the offence was "not at the most serious end of the scale" but still warranted a nine-month ban. Cilic has said he will appeal against the decision to the court of arbitration for sport.