The Northern Ireland international was struck just below the left eye by the projectile, and both he and manager Tony Pulis were outraged by the attack.
The Football Association is to investigate the incident in which West Bromwich Albion midfielder Chris Brunt was struck by a coin thrown by one of the club's supporters following the FA Cup tie at Reading on Saturday.
The coin struck Brunt just below his left eye as he went to applaud the visiting contingent seconds after the final whistle, prompting the Northern Ireland international to gesticulate angrily as he sought to find the culprit.