Ukrainian tennis player Dayana Yastremska failed to have her provisional suspension for a failed dope test lifted on Wednesday, ruling her out of the Australian Open.
The decision means that Yastremska, who is ranked 29 in the world, will not be able to play in the season-opening Grand Slam event in Melbourne from Monday.
The 20-year-old had flown to Australia, where she quarantined for two weeks, in the hope that her ban, handed down after testing positive for a banned anabolic agent used in male infertility treatment, would be lifted.
"I know my presence in Australia has raised some concerns," Yastremska said in a statement.
"The urgent procedure with the ITF Independent Tribunal and the CAS could have lifted my suspension which would have enabled me to compete at the Australian Open.
"That's the reason I was allowed to travel here. I intend to return all the expenses engaged by Tennis Australia on my behalf."
The International Tennis Federation (ITF) said Yastremska tested positive for the outlawed mesterolone metabolite in an out-of-competition test last November.
She first appealed to the ITF's independent tribunal which upheld her ban on January 23.
CAS said in a statement that the suspension "remains in force until a final decision is rendered by the ITF".
At the time of the original ban, Yastremska took to Twitter to deny any wrongdoing.
"I firmly state that I have never used any performance enhancing drugs or prohibited substances," she wrote.
"I'm astonished and under shock, particularly given that two weeks prior to this test on November 9, I tested negative at the WTA event in Linz."
Yastremska has won three WTA titles in her career, with her best Grand Slam performance a run to the fourth round at Wimbledon in 2019.
She added Wednesday: "I remain determined to clear my name."