Manufacturing problems at South Korea's LG Display could force Apple to rely on rival Samsung Display for high-end and costly smartphone screens.

Apple has been trying to find a second OLED supplier for its high-end iPhones besides Samsung Electronics' display unit. However, The Wall Street Journal reports that LG Display, which is the leader in OLED displays for TV sizes - appears to be struggling to bring that experience over to smaller smartphone displays.

Apple's reliance on a single OLED supplier means Samsung controls pricing on the displays that Apple is buying.

LG returned to using OLED phone displays for the V30, but the quality of the display wasn't very good. LG has also been supplying OLED displays for Google's Pixel 2 XL handset, but still the quality varied across the devices.

Meanwhile, Apple fell for the third day after analysts at Morgan Stanley cut their forecasts for iPhone shipments, adding to concern about the tech giant's primary source of revenue ahead of quarterly earnings in May.

Morgan Stanley analyst Katy Huberty lowered her projections for iPhone shipments by 1 million in the quarter ending in March and 6 million for the current quarter. Huberty now sees shipments for fiscal 2018 of 210 million, down from an earlier estimate of 217 million.

The note comes a day after Taiwan Semiconductor Manufacturing Co. cut its revenue growth forecast for this year to 10 percent annually on weak demand for Apple's iPhones and uncertainty over cryptocurrency mining demand. As Apple's main chip supplier, TSMC's revenue forecast revived fears that the iPhone X, Apple's flagship $999 handset, may already be losing momentum a quarter after its release.

Apple is the Taiwanese chipmaker's biggest client. Based on TSMC's annual financial report released yesterday, Apple contributed 22 percent to its total revenue of NT$214.2 billion last year.