Police have made an arrest after the midfielder was hit on the face by the coin, thrown from a section housing West Brom fans, after he went to give his shirt to a supporter at the end of the Baggies’ 3-1 FA Cup fifth-round defeat.
QPR have begun their own investigation into the incident on Saturday, while Birmingham have promised stern action against anyone found responsible.
A QPR statement said: “A coin from the School End stand, in which the visiting supporters were situated, was thrown towards the Rangers players as the Rs celebrated their second goal in our Sky Bet Championship fixture at Loftus Road.
“The club will continue to review video footage and liaise with the Metropolitan and West Midlands police.”
A Birmingham spokesman said: “If anybody is found to have thrown a coin, we will take the strongest possible action. As a club, we utterly condemn that sort of behaviour.
“We will be liaising with the relevant bodies, including West Midlands Police, to investigate such allegations.”