Analysts in America are starting to express concern about the continued expansion of Starbucks.

The Seattle-based coffee company is adding three to four shops to its 5,000-store empire every day with an eye toward expanding to 20,000 in coming years.

However, commentators are worried that the company is spreading itself too thin as growth in sales at stores that have been open less than a year hovers just above zero.

"I think the company is expanding too rapidly and they don't have to," said Doug Christopher, an analyst at Crowell Weedon. "Starbucks has a tremendous competitive advantage with the quality of their coffee and the strength of their brand. Nurturing that would get their sales-per-store higher and would get their stock price a lot higher."

The company is due to announce fourth quarter results next Thursday.