They probably should give a bit more thought than usual to avoiding trouble as they travel to Champions League group stage matches in Moscow in the coming days.

One fine idea might be to hold off on consuming copious amounts of alcohol in the hours before kickoff.

Why? Beside the calories?

Because English club fans will be far from home tomorrow and Wednesday nights, first with Liverpool taking on Spartak Moscow and, a night later, with Manchester United at CSKA, another Moscow club.

And in case any of the estimated 2,000 Liverpool/United fans who are traveling to Russia were unaware of what authorities in Moscow have in mind … the head of security for the Russian Football Union warned that those who behave badly might face “a long stay in Russia.”

English and Russian fans have some recent history, going back to last summer, when they clashed twice, first in Marseille and then in Lille, at the 2016 European Championships in France.

England fans of the 21st century are not to be confused with the masses of hooligans who made life so difficult for regular fans — not to mention the authorities — back when traveling in the 1970s and 1980s.

The traveling fans now are not the hard-core thugs of days past, but neither are they angels.

It can be expected that the traveling fans, many of them, will be drinking hours before the game, and singing, and may be thinking in terms of taunting their hosts.

The Russians have indicated they will not have much patience for England fans who get out of line.

In Marseille, last June, a batch or Russians who had a para-military cast to them, badly roughed up some England fans and, after, crowed about how the English were “old and fat” and no match for them.

Liverpool and United fans traveling to Moscow probably will be more softies, perhaps emboldened by drink to push the envelope.

Anyway, the Russian authorities have given the English fair warning.

Said Vladimir Markin, of the Russian League’s security arm, to Tass:

“I don’t want to scare anyone but I warn those who plan to come here not to support their side and see the country but to commit hooliganism: The law is the same for all, not just for Russians.

“Those who break it will face a suitable punishment, possibly in the form of a long stay in Russia, in conditions our guests won’t like.”

According to The Guardian, a British daily, both Liverpool and United have advised their fans not to wear club colors or travel alone in Moscow. Fans also have been told to expect “a heavy security presence” at the two matches in Moscow.

Now we wait to see if the lads can stay out of trouble.