SAN FRANCISCO (REUTERS) - Shares of Apple supplier Cirrus Logic slumped 18 per cent on Thursday after the chipmaker said in a filing it faces growing pricing pressure in the smartphone market.

Cirrus said in the filing it expects gross margins in the mid-40s. It did not indicate what period it was referring to and a spokesman did not immediately reply to a request for comment.

For the current quarter, Cirrus has said it expects gross margins between 50 per cent and 52 per cent.

In the filing, it also said revenue for the fiscal year is likely to be impacted by a drop in average selling prices.

"Potential dual-sourcing at Apple, margin pressures at Apple, low cost iPhone bill-of-materials pressures, lack of content-increase opportunities and pricing pressure from Apple are all now much larger question marks," Oppenheimer analyst Rick Schafer said in a note to clients.

Apple, under growing pressure from sellers of low-cost Android smartphones, represents about 85 per cent of Cirrus'revenue.

Cirrus' stock was down 18 per cent at $18.09.