According to a report in The Grocer, Jim Waller, M&S commercial director of food, discussed the retailer's plans in a speech at an industry networking event. He said that for the venture to work, the retailer would have to sell a full offering of groceries.
M&S currently uses its food halls to sell a range of about 3,000 own-label products. However, selling just these online would make the venture less financially viable, so the retailer would offer customers multiple brands.
Waller said: "If you are going to put together an online operation you need to provide a full grocery offer.
"Whether we do it with a partner is up for consideration. We can't afford to bury our heads in the sand about online."
Waller did not give a timescale for the initiative, but said it would be unlikely to launch this year.
A spokesman for M&S denied it is planning to launch online grocery delivery, saying there was no short-term prospect of the service.
Online grocery sales is a fast-growing market. According to research from Verdict, sales rose by 33% in 2007, while supermarket sales growth was only 3.7%.