Former world number four Jelena Dokic has gone missing in Zagreb, with the Serbian media reporting that she may have been kidnapped.

Dokic's father Damir, claims that his daughter's former coach Borna Biknic, and his brother Tino, who is a former boyfriend of Dokic, are behind the disappearance.

"I'm very worried for my daughter," he told Serbian paper Kurir.

"Jelena will never admit that she was kidnapped or made to stay in Zagreb, but I think it is crystal clear that the Bikic brothers are behind all this."

Dokic had been training in Germany with former Croatian tennis player Nikola Pilic before making the trip to Zagreb, but the coach says he is now completely in the dark about Dokic's current situation.

"When Jelena went to Zagreb she said that she would get in touch with me, but she hasn't, and I think there is no doubt that the Bikic's brothers are behind all of this," he said.

Serbian tabloid Kurir is also reporting that Jelena had phoned her mother on Monday claiming that she would not be returning to Germany to train with Pilic, after having apparently told her just a day previously that she was only in Zagreb to pick up some winter clothes.

A former Wimbledon semi-finalist, Dokic's career has been in freefall in recent years and she has struggled with numerous comeback attempts. She is currently ranked 583rd in the world

Her last tournament was the $10,000 Ismaning competition earlier this month where she made the semi-finals.

Her father, Damir has been a highly controversial figure in the past, with his unruly behaviour at events having seen him being previously banned by the WTA.