The 18-year-old will work with the former coach of Justine Henin and Li Na.
Andreescu is the youngest to make the WTA Finals field in a decade.
The Serb has now logged more weeks at No.1 than all but two ATP players.
Hall of Famer has high praise for Daniil Medvedev.
The World No.1 will have to be at his best early in Tokyo.
The king of clay played host to his Laver Cup captain Björn Borg.
The World No.1 will be back in action next week at the Rakuten Open.
