Boxing: Wladimir Klitschko to fight Francesco Pianeta

Wladimir Klitschko retained his heavyweight titles with a knockout (AP)

Wladimir Klitschko will defend his four world heavyweight title belts against his former sparring partner, the German-Italian Francesco Pianeta in Mannheim on 4 May.

Klitschko, who holds the IBF, IBO, WBO and WBA crowns, used the 28-year-old Pianeta as a sparring partner last year. Pianeta is undefeated in 29 professional fights.

"I have a lot of respect for Pianeta because he is young and has a big fighting spirit," said Klitschko, 36. It will be his 14th defence in his second stint as a world heavyweight champion.