Novak Djokovic's grandfather in-law kidnapped and robbed in targeted attack

The grandfather of Jelena Djokovic, the wife of tennis star Novak Djokovic, has been found tied up in a field after robbers reportedly broke into his house in Serbia.

Djokovic's spokesman said the family is in "complete shock over what happened" to 85-year-old Miloslav Radisavljevic.

They said attackers broke into Mr Radisavljevic's house, kidnapped him and took him to a field several kilometres away.

Police said they found a man early on Thursday tied to a power pole close to his house in Ljig, about 80km south of Belgrade.

The man told police he was also robbed by the two masked attackers of about 220 euros ($A347) and a mobile phone.

Police said the man had no visible injuries.

According to Serbian news site Blic, the mayor of Ljig, Dragan Lazarevic, said he had received text messages asking for two million euros in ransom from the robbers during the ordeal.

After Djokovic's recent Wimbledon victory, where he won $3.9 million, he thanked his family for their support.

"My whole (more or less) was about tennis until I became a father and husband. Everything I did was aimed at tennis success," he said in the emotional post.

"When I became father and husband, my “world” evolved. It didn’t change, it evolved into something more beautiful.

"It takes learning and openness to reach that “golden balance” in life which everyone is in pursuit for. For me it was balance between tennis, priorities and family."

Djokovic wife is the president of his foundation. They have two children, Stefan (4) and Tara, born last September.