Asos has warned sales will continue to fall in the year ahead – by much as 15% – after delayed results revealed it slumped to a near £300m annual loss.

Analysts have expressed fears that the online fashion site will need to raise new cash – potentially through the sale of its Topshop brand – with net debt including leases now at £648.5m, up from £533m a year before.

José Antonio Ramos Calamonte, Asos’s chief executive, said it had made “good progress” in “a very challenging environment” and would continue to bring in new more fashionable stock and invest in its brand.

The company plans to spend £30m more on marketing and said it was going “back to fashion” with its products “geared around fashion and excitement”.

Asos has been hit by a shift away from buying online since the Covid pandemic restrictions ended, as well as heavy competition from companies such as the fast fashion online specialist Shein and retailers with a combination of stores and online retail, such as H&M and Zara.

Sales fell 10% to £3.5bn in the year to 3 September as profits slumped to £296.7m from £32m a year before, according to the Asos results released on Wednesday – a week later than originally planned.

Calamonte said that clearing of unwanted stock throughout the year ahead would “remain a drag on sales growth and profitability”. Sales are expected to fall by between 5% and 15% but the company said it expected to reduce net debt by generating cash from the sale of stock.

He said Asos had “significantly improved the core profitability of the business” during the year and was now “taking decisive action in [the current year] to clear stock brought in under our old model while substantially improving our speed to market and investing in our brand, reminding our customers what we’re really about: fashion”.