A defect in some touch panels made by Wintek for the next-generation iPhone could leave the manufacturer struggling to meet quotas and potentially mean that Apple won't have as many units at launch as hoped, it has been claimed.

Digitimes reports that sources in the iPhone supply chain have expressed concerns about Wintek's ability to meet its obligations to ship the touch panels on time. Wintek will supply between 20 and 25 percent of touch panels for the next-generation iPhone, while Taiwan-based TPK Holding accounts for 60 to 65 percent.

However, Wintek said that all of its products are being delivered on schedule, according to the report.

The issue is known as a 'delayed bubble' - and involves a problem in the lamination process. The problem is apparently very difficult to pick up immediately after the lamination, but more easily noticable when it comes to assembly.

Apple seems to be gearing up to make an announcement about the next-generation iPhone on 4 October, with some expecting a launch of the device - whether it be the iPhone 4S or iPhone 5 - on 21 October.