Stars gear up for the holiday season pumping up.
Former No. 1 tabs Zverev as future No. 1 and offers alternate view on champions coaching.
The former U.S. Open runner-up owns 35 titles between singles and doubles.
World No. 2 hasn't officially retired from Swiss Davis Cup squad.
The Spaniard will take over for Manolo Santana in 2019.
Team Canada also has a new captain for 2018.
Torben Beltz coached Angelique Kerber to two Grand Slam titles.
