SoftBank Group Corp. is nearing a deal to invest about $400 million in a health care portal run by Ping An Insurance (Group) Co. ahead of the Chinese company's initial public offering, according to sources with knowledge of the matter.

The Ping An unit, known as Good Doctor, aims to file an IPO application with the Hong Kong stock exchange as soon as the end of January, the sources said, asking not to be identified discussing a private deal.

It wasn't immediately clear whether the Good Doctor investment would be made by SoftBank itself or through the Vision Fund that it manages.