Hanover (Germany), Dec 31 (DPA) German tennis player Nicolas Kiefer, a former world number four player, said on Thursday he is retiring from tennis with immediate effect.

Kiefer, 32, said on his homepage and in an interview with Die Welt daily that he wants to spend more time with his baby daughter.

"The career on the ATP Tour is over," Kiefer said on his website. "My biggest aim in life became true on August 11 ... with the birth of our daughter Mabelle Emilienne."

He told Die Welt: "It is time to start a new chapter in life after 15 years. Come on Kiwi, you had a super career, met many great people, saw many countries and learnt a lot. It's enough. Now you are a father and have a daughter."

Kiefer said he decided over the past days to hang up his racket.

Once hailed as a successor of Boris Becker, Kiefer was a junior champion at the Australian and US Open in 1995. He won six tournaments on the ATP Tour, was ranked fourth in 2000 and also has an Olympic doubles silver medal from 2004.

However, a string of injuries denied Kiefer further success. He is currently ranked 722nd.

"There can only be one Boris Becker. He was still the biggest motivator for me, I learnt the most from him. I am very grateful for that. Sometimes I just lacked this little bit which separates a Boris from someone who is not quite as successful," Kiefer told Die Welt.

Kiefer said he plans to continue in sports as an over-32 player at football club Hanover 96 and through his sports management studies.

He did not rule out a future in tennis as manager or advisor, or working for the German tennis federation.