The defender was left bloodied but unbowed as the Reds celebrated during the remarkable climax and the manager was upset to also see a fan attempt to confront the centre-back with Joe Hart's quick thinking thankfully stopping the spectator in his tracks.
City later issued a statement revealing the club will co-operate fully with the local police in order to punish any offenders, while the Football Association confirmed they are investigating the incidents.
"It was disappointing that a supporter ran on the field after Rio had been hit by a coin in the eye," the manager told MUTV at the Etihad Stadium. "It's a bit disappointing. The game didn't deserve that.
"I don't know whether they're going to stitch it or not. The same thing happened at Chelsea with all the carry-on when half a seat hit Michael Carrick and coins and lighters were thrown on. The game doesn't need that."
Ashley Young agreed with the manager that it was an unpleasant way to end an absorbing clash with the eyes of the world watching on TV.
"It could have taken Rio’s eye out and you’ve seen the cut on his head," said the winger. "When 'Wazza' was taking a corner there were so many objects being thrown onto the pitch as well and, on another day, if the pitch had not been so wet, the fan who came onto the pitch wouldn’t have slipped over and could have attacked Rio. It’s not nice to see that and hopefully it’ll be dealt with."