#4 Zverev spent three years playing at the ATP Challenger and ITF circuits
During the twilight of 2011, Zverev had a miserable decline in form with his ranking falling below 200 and going as low as 280 during the first week of November. At this point, he decided to take a break from the ATP World Tour and instead play on the ATP Challenger Tour and ITF Futures tournaments.
The southpaw went on to play in those tournaments for a span of three years between 2012 and 2015. During this time, he did not win any singles titles but won two doubles titles on the Challenger Tour.
In the Futures circuit, he won one title at the USA F28 Futures tournament. However, it was during this time that his ranking dropped as low as 1067 during 2015. However, he returned to the main tour in 2016.