Stefanos Tsitsipas sees room to move in Miami.
Acapulco champion sees game improvement since Flushing Meadows final.
World No. 3 shares her goals.
Former No. 1 joins Big 3 in withdrawing from Miami Open
World No. 40 playing with the Babolat Pure Aero+ racquet.
"You have a problem with Andy Murray playing? Absolutely he has earned it," Hall of Famer Martina Navratilova said.
Eight-time champion joins Novak Djokovic, Rafael Nadal and Roger Federer in pulling out.
