The American will not make the trip to Australia last year thanks to a positive Covid test.
The Austrian will be without his coach for a few weeks at least.
Rafa Nadal's coach, former world No. 1 Carlos Moya, won't make the trip to Melbourne.
World No.42 will play with Dunlop SX 300 racquet.
The Chilean hopes to return to play the South American swing at the end of February.
Serena tunes up for AO with total focus.
Michael Joyce, who coached Maria Sharapova and Victoria Azarenka, joins USTA player development.
