** PainChek PCK.AX plunges as much as ~31% to A$0.038; marks biggest intraday pct drop since June 18, 2017
** Stock hits lowest since May 7
** Medical devices maker flags potential delay in U.S. FDA clearance for its pain assessment app
** Expects clearance by mid-to-late September instead of the first half of 2025 anticipated earlier
** About 14.3 mln shares traded in stock's busiest day since February 18, 2021
** PCK last up 21.8%, taking YTD gains to 48.3%
(Reporting by Keshav Singh Chundawat in Bengaluru)
((Keshav.SinghChundawat@thomsonreuters.com;))