NEW YORK (TheStreet) -- GT Advanced Technologies (GTAT) shares are down -3.5% to $15.48 on Monday after analyst at CLSA said that they see a risk to the company's 2014 guidance while maintaining their "outperform" rating and $18.50 price target on the stock.

The firm believes that the company's sapphire supply to Apple (AAPL - Get Report) indicates weak yields, limiting supply and threatening  the company's EPS and revenue forecasts for the year.

CLSA lowered the company's material revenue guidance to $200 million from $400 million this year and to $600 million from $750 million next year. It also lowered its EPS guidance to -30 cents from 10 cents this year and to 50 cents from 65 cents in 2015.

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