Marketa Vondrousova, the 2023 Wimbledon champion, said on Friday she was facing a doping investigation after failing to submit a sample during a check last December.
The world number 46 risks up to a four-year ban from tennis for refusing to let in a doping control officer ringing the bell at her Prague home.
But she said the check was not standard as the officer from a German agency failed to identify herself.
"The recent doping control incident happened because I reached a breaking point after months of physical and mental stress," the 26-year-old injury-prone Czech said on Instagram.
She told the Sport daily that it "was stressful to see someone I didn't know asking to enter my living room without showing authorisation".
"At the moment, I was thinking this could be anyone," she added, explaining why she refused to let the officer in.
Vondrousova said she had dealt with injury, pressure and "ongoing sleep issues that left me feeling exhausted and fragile" for some time.
KVITOVA CASE ON HER MIND
She also mentioned the case of her compatriot and two-time Wimbledon champion Petra Kvitova, who suffered a career-threatening injury to her hand when she opened the door to a knife-wielding stranger in 2016.
Kvitova took five months to recover from cuts to her left hand. The perpetrator was sentenced to 11 years in jail for serious battery and illegal entry into the player's flat.
"When someone rang my door late at night without properly identifying themselves or following protocol, I reacted as a person who felt scared," Vondrousova said on Instagram.
"In that moment, it was about feeling safe... after what happened to Petra, we don't take strangers at our door lightly."
Vondrousova's lawyer Jan Exner told AFP that "the doping control was simply not standard and therefore Marketa had a reason not to submit the sample".
"You simply face pressure, you even get death threats for ruining someone's bet slip. So the non-standard doping check sparked an acute stress reaction in Marketa which experts – both Czech and international – have confirmed," he added.
Exner said he would try to convince the International Tennis Integrity Agency (ITIA) that this was a valid reason for Vondrousova to decline to submit the sample.
"The proceedings are underway. There will either be a hearing or we will try to agree with the international bodies. We should know more by the summer."