The head of the British police contingent at Euro 2012 has urged Ukrainian officers to "make an example" of isolated racist incidents.
Assistant Chief Constable Andy Holt said there was "not much you can do" if large groups of supporters are involved in abusive chants and actions.
But he claimed the arrest of individuals could act as a deterrent to stop the problem becoming widespread.
At an open training session in Krakow, Poland, on Wednesday, Dutch players were subjected to monkey chants with Holland captain Mark van Bommel branding the incident "a real disgrace".
Mr Holt said: "If individuals engage in inappropriate disgusting racist behaviour and there are lots of them, the reality is practically there's not much you can do on the day.
"You might be able to take CCTV footage and decide to prosecute after the event. But if you've got a football stadium with lots and lots of people engaging in criminal behaviour, then it is very difficult in the heat of the moment to try and do something and do it safely and appropriately."
He hopes the Ukrainian police will act at the first sign of a problem.
"One of the things that we've been advising is if you've spotted individuals doing something inappropriate that you tackle that very quickly and swiftly and make an example.
"If people think, 'oh my goodness, that guy made a chant, made a gesture, threw something - maybe a banana on the pitch or something - and look he's now heading to the cells', in my experience that's always a deterrent.
"But you need to do that when you can, rather than when there's 3,000 doing it."