Her manager Ji Lingling did not confirm or deny the rumour.
Asked if the actress is engaged, Apple Daily Taiwan quoted Ji as pausing and then saying: 'Well...'
She again hesitated without commenting.
Zhang's romance has been out in the open since January last year when she and Nevo, 42, kissed at a ball match.
The 29-year-old has not confirmed the romance but the two have been seen together at parties and film festivals.
Late last year, Chinese reports said the couple had registered their marriage in the United States.
Meanwhile, the actress is set to go behind the camera with her new film studio.
Deng reportedly told American Vogue in its latest issue that she has teamed up with Zhang and a friend, Florence Sloan, to run the studio.
Deng and Zhang have been friends for about five years, and the actress had met Nevo on her boat, the tycoon's wife said.
Asked about the project, the actress reportedly said: 'I've been acting and learnt quite a bit. I hope to learn more of different things.'
Reports said the first film to be rolled out by the venture may be an adaptation of writer Shan Sa's novel, Empress, about Chinese empress Wu Zetian.