Former world No 1 Simona Halep has been charged with a further breach of anti-doping rules, the International Tennis Integrity Agency (ITIA) confirmed on Friday.
Romanian Halep has been provisionally suspended since October 2022 for testing positive for the banned substance roxadustat at the US Open in August last year.
On Friday, the ITIA said that the two-time Grand Slam winner has been further charged "relating to irregularities in her Athlete Biological Passport (ABP)".
It added that the "charge is separate and in addition to the existing roxadustat charge from August 2022 which triggered Ms Halep's original provisional suspension".
The ABP programme is a method by which anti-doping organisations monitor various blood parameters over time, to identify potential doping violations.
Nicole Sapstead, Senior Director for Anti-Doping at the ITIA, said: "We understand that today's announcement adds complexity to an already high-profile situation.
"It would be inappropriate for us to comment on specifics until the conclusion of the process, but we will continue to engage with the Sport Resolutions independent tribunal and Ms Halep's representatives as expeditiously as possible."
Halep, 31, said after her positive test last October that she would "fight until the end" to clear her name, as she awaits a doping hearing scheduled for 28 May.
"Knowingly, I have not taken any banned substance," the Romanian star told tennismajors.com in an interview published last month.
"I am a big supporter of clean sports and have always been against doping. I had no clue at the beginning about where this substance came from."
Halep had climbed back into the world's top 10 before she was suspended having dropped out of the top 20 in 2020 following injury problems.
But the former French Open and Wimbledon champion has tumbled to her current mark of 30th.
Roxadustat is a drug that stimulates the production of red blood cells and is used in the treatment of patients with kidney problems.