ASOS PLC Robertson has informed the company's board of his decision, but will remain on the board as a non-executive director, Sky News said.
ASOS Chief Operating Officer Nick Beighton is expected to succeed Robertson, the newspaper said, citing sources.
The announcement will likely be made to the London Stock Exchange before the market opens on Wednesday morning, Sky News said.
ASOS could not immediately be reached for comments.
The company named Helen Ashton as Chief Financial Officer in April, who took over from COO Beighton.
The company is popular with internet-savvy twentysomethings as well as celebrity fans such as U.S. First Lady Michelle Obama and British singer Rita Ora.
(Reporting by Rama Venkat Raman in Bengaluru, editing by William Hardy)
