Following a poor forecast earlier this month, analysts and investors expressed concerned about Apple's prospects and said its smartphone sales might be stagnating.
This led Apple's shares to drop by 5 percent.
Lumentum's outlook comes a week after Nikkei reported that Apple was cancelling a production boost for its iPhone XR line, and less than two weeks after Apple's fourth-quarter results showed tepid unit sales growth. The iPhone XR is also - whether Apple wants to admit it or not - the company's answer to the influx of powerful-but-affordable Android devices.
Analyst Ming-Chi Kuo has been keeping his finger on the pulse of Apple component suppliers and that pulse is slowing the total expected shipments of the iPhone XR have been revised down by as much as 30%.
"We think investors should consider Lumentum's updated guide as reflecting as much as a 30% cut in Apple orders", Wells Fargo analyst Aaron Rakers said in a note to clients.
These reports come shortly after Apple announced that it would no longer provide iPhone unit sales, one of the key signals that analysts use to evaluate Apple's business.
Apple's stock dropped yesterday when news broke that one of its main suppliers reduced its outlook for the rest of the year, citing reduced orders from one of its biggest customers.
The firm hoped the iPhone XR would persuade owners of older iPhones to switch to the newer model, which costs $749 (£749) - a sizable discount from the $999 iPhone XS and the $1099 XS Max.
Apple has lost $120 billion in market capitalisation since the last trading day of September, and many analysts are warning that the brief days of Apple being a trillion dollar company are over. Apple said it preferred to focus on the company's transition to a services company, with regular recurring revenue.
Apple CEO Tim Cook was directly asked about this possibility during Apple's most recent conference call. The company also said it would stop providing unit sales for iPhones, iPads, and Macs in fiscal 2019, a step Nomura Instinet said raised "the spectre of a sustained iPhone downturn".
"A year ago AAPL looked like a table-pounder when iPhone units were weak", Guggenheim wrote in its note on Wednesday.
"This year Apple well and truly is the stock market once again", Cinko writes, "and its price action lately has been stirring up troubling signs about what might be next for equities".
