Ljubicic reached a career-high of world No 3 and won ten titles in his career before retiring in 2012.
Milos Raonic was the first player the Croatian coached and their relationship lasted two years before he became Federer’s coach in 2016.
Under Ljubicic’s helm, Federer has enjoyed a remarkable resurgence winning three Grand Slam titles, including the recent Australian Open.
Federer’s long-term coach has been Severin Luthi but he has co-coached the 20-time Grand Slam champion with Ljubicic.
And the two coaches were in the stands in Rotterdam as Federer became the oldest world No 1 in men’s history.
But Ljubicic says his coaching methods are based around listening to the player to get the best from them.
He told ATPWorldTour.com: “When you talk about coaching at the highest level, you have to listen a lot.
“The most important thing is to understand a player. Listen at the beginning, but then listening in general to understand and ultimately help a player.
“When you start with a player in the middle of a season, such as Milos, you can’t step in and say, ‘I want to change everything, because this is how I did it.’ I feel that it doesn’t work like that.
“You see, if you are coaching a player, who has been around for a while, he has his own patterns and ideas.
“His own opinions on a lot of stuff, and you have to pick your fights on what you think will have the biggest impact on a game or the result.”