Former French Open champion Michael Chang has been hired by Kei Nishikori as a part-time coach.
The 41-year-old American will spend around 20 weeks in an advisory role with the Japanese world number 17.
Meanwhile, Dante Bottini will remain as Nishikori's full-time coach.
Chang became the youngest male winner of a Grand Slam when he triumphed as a 17-year-old at Roland Garros in 1989.
