Two-time Grand Slam champion Simona Halep was charged with a second doping offense due to “irregularities in her athlete biological passport”.
The Romanian, 31, has been suspended since October after testing positive for a banned substance at the US Open.
His additional charge is different from the one he is has been suspended for.
The athlete’s biological passport program collects and compares biological data to detect differences over time that suggest possible doping.
The suspension of former world number one Halep last year was imposed after she tested positive for roxadustat, an anti-anemia drug that stimulates the production of red blood cells in the body.
The International Tennis Integrity Agency (ITIA), which is responsible for testing within the sport, said it would try to resolve the latest case as soon as possible, but did not indicate how long it would take.
Nicole Sapstead, the ITIA’s senior director for anti-doping, said: “We understand that today’s announcement adds complexity to a high-profile situation.
“From the start of this process – and indeed any other ITIA – we remain committed to engaging Ms Halep in an empathetic, efficient, and timely manner.”
Halep, the 2019 Wimbledon champion, said in October that “cheating never crossed her mind” and claimed that the failed test was due to a “contaminated” supplement.
In April, Halep spoke for the first time since his suspension, saying he was disappointed with the time it took to resolve the case but ITIA said “the process is ongoing”.
Investigations into failed ITIA tests are often a complicated process, especially if a player refuses to take a known substance.
It is common for these cases to take several months to resolve.
In such cases, a player can produce evidence to refute or explain the failed attempt, which Halep says he did.
This will lead to further investigation and testing by the ITIA, leading to the process being further expanded.
Halep, who was ranked ninth when the ban came into effect, is one of the most high-profile tennis players to fail a drug test, and the most famous since the Russian five-time major champion that Maria Sharapova was banned in 2016.