The retailer is considering holding a second "one-day spectacular" on December 4, two weeks after its last sale, according to a report in The Daily Telegraph.
It is understood to be in talks with media buying agencies about booking ads to promote the second event next week.
A spokeswoman for M&S refused to confirm the sale but did not rule it out either, saying that people would have to "wait and see".
M&S was pleased with last week's sale, its first pre-Christmas sale in four years, which led to queues at the cash desks.
It was hailed a success by chief executive Sir Stuart Rose who said: "It seems to have touched the spot. It's a riot."
M&S is one of many retailers offering pre-Christmas discounts this year including House of Fraser which is planning a two-day sale on Thursday and Friday this week, with prices cut by 40%.
Discount vouchers are circulating on the internet with Woolworths knocking 20% off for "friends and family" who print off the voucher and Selfridges employing a similar tactic.