The 8-time major champion arrived on Saturday to join forces with Grigor Dimitrov in Paris.
The Czech won five titles, reeled off two mammoth win streaks and claimed 47 victories in 2018.
The Dane revealed the diagnosis after her season ended on Thursday at the WTA Finals.
The Swiss scampers in style to win a gorgeous point against Filip Krajinovic.
Hall of Famer says it's a matter of time: Serena will win more majors.
The Czech duo becomes the 40th and 41st WTA doubles No.1s.
