Wintek Corp. (2384:TT), a top Taiwanese panel manufacturer and leading supplier of Apple (NASDAQ:AAPL) iPhone touch panels, announced Tuesday a staggering drop in month-on-month sales.

This has led to speculation that the company may no longer be one of Apple’s top panel suppliers. Apple has been rumored to be featuring in-cell touch panels for the sixth-generation iPhone, a technology Wintek does not provide.

Brian White, an analyst from Topeka Capital Markets, said that Wintek’s 33.6 percent month-on-month sales decrease in June, was the biggest drop he had observed in close to four years. He did add that Wintek’s sluggish performance may indicate a change in the guard in terms of Apple suppliers, but not necessary a possible decrease in Apple touchscreen device sales.

In more disconcerting news for the Taiwanese company, Wintek stocks hit an in-day low of 15.80 on Tuesday, which is a far cry from their 52-week high of 38.64 posted on July 21, 2011.

Signs of Wintek falling from favor in the eyes of Apple started a few months ago, when it was reported that the Cupertino, CA company may be using thinner in-cell touch panels on the iPhone 5. Some of the companies considered by Apple include Toshiba Mobile (6502:T) and Sharp Corp. (6753:T).

White also mentioned that over 50 percent of Wintek’s sales came from Apple, as they had previously been a primary supplier of iPhone and iPad touch panels.