Novak Djokovic failed to train hard enough and will not regain the No 1 world ranking "unless he puts in the hours", former coach Boris Becker said on Wednesday, a day after the pair ended their working relationship.

Djokovic has won 12 Grand Slam titles - six under Becker - but on Tuesday the Serb confirmed rumors that he and the German legend had parted ways after three years together.

Becker said Djokovic's need to spend more time with his family had derailed him on the court.