Despite the firm's record fourth quarter profits, its iPad line has lost ground on rival slates such as Amazon's Kindle Fire, according to figures from iSuppli.
The iPad shifted 15.4 million units during the final months of 2011, though its market share has declined from 64% to 57% since then.
Amazon's Kindle Fire is the device's closest competitor, selling 3.9 million units over the Christmas period, setting its market share at 14%. The Android tablet is considered a budget-friendly alternative to the iPad, though the platforms target different market sectors.
Earlier this week, Apple CEO Tim Cook hit out at what he described as "cheap" competitors to the iPad, claiming that consumers "hate" them.
"A cheap product might sell some units. Somebody gets it home and they feel great when they pay the money, but then they get it home and use it, and the joy is gone," he said.
"The joy is gone every day that they use it until they aren't using it anymore. You don't keep remembering 'I got a good deal' because you hate it."
The Kindle Fire is yet to launch outside the US, with Amazon remaining tight-lipped over the possibility of a European release.
Apple's third generation iPad is expected to be announced on March 7.