A British tennis player who was forced to pull out of Wimbledon due to a mystery illness fears that she may have been deliberately poisoned by someone hoping to sabotage her tournament chances.

Gabriella Taylor, 18, was forced to retire from her girls’ quarter-final against the U.S.’s Kayla Day on July 6 after she became unwell, the BBC reports.

She was seen looking ill on the court and repeatedly held her stomach in pain until she eventually conceded the match, believing she had food poisoning.

The current world number 381, from Southampton, then spent four days in intensive care. Her mother, Milena Taylor, told the U.K.’s Daily Telegraph that her daughter was “close to death”.

Now officers have confirmed that they are carrying out a criminal investigation into allegations of poisoning with “intent to endanger life or cause GBH”, after doctors eventually diagnosed a rare strain of leptospirosis, a bacterial infection spread to humans by the urine of animals, particularly rats.

Mrs Taylor told the Daily Telegraph that Gabriella “was staying in a completely healthy environment” and for her to get ill due to rat urine was “just impossible”.

Theories that the 18-year-old was sabotaged by a rival player or coach or that she was targeted by a criminal betting syndicate are being explored.

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Write to Kate Samuelson at kate.samuelson@time.com.