The Reds boss added: "It is good that Uefa have acted. But the problem is that it is just one person out of thousands who decides to do something like that, so how can you control it? It is not easy to stop these things.
"It is difficult to control everyone, if someone wants to do something like this then it is hard to stop.
"You can fine the club and look for solutions afterwards, but you cannot control everything."
Gerrard headed the winner - his 30th European goal and fifth in this season's competition - in the first half to send his team through to the final 16 of the Champions League.
Earlier this season, Chelsea striker Didier Drogba was given a three-match domestic ban by the Football Association for throwing a coin back into the crowd when the Premier League leaders lost in the Carling Cup to Burnley.
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