Klitschko, who holds the IBF, IBO, WBO and WBA crown had used the 28-year-old Pianeta as a sparring partner last year.
The 36-year-old Ukrainian's record stands as 59 wins and three defeats after his three successful title defences in 2012, including a November victory over Poland's Mariusz Wach.
Pianeta, who at 1.93 metres is five centimetres shorter than his opponent, is still undefeated with 28 wins and one draw.
"I have a lot of respect for Pianeta because he is young and has a big fighting spirit," the 36-year-old Klitschko said in a statement.
Klitschko's older brother, Vitali, holds the WBC crown.
"I was briefly his sparring partner last year and I noted where his weaknesses are and how best to exploit them," said Pianeta. "I understand many see me as an outsider and that is fine but I will knock Klitschko out and turn the world of boxing on its head." (Reporting by Karolos Grohmann, editing by Justin Palmer)