Western business that have avoided the country due Western-imposed sanctions over tensions with Ukraine are mistaken, he said.
"I am a business man, I started to invest in Russia back in 1995 when we installed the first advertising bus shelters in St. Petersburg, so St. Petersburg is my home town when it comes to Russian investment," he told CNBC, speaking at the St. Petersburg Economic Forum.
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"If you don't have the guts to invest here you better stay at home, but it is a big market," he said.
The outdoor advertising agency employs some 3,000 people in Russia and owns 25 percent of the country's largest outdoor advertising company. Decaux said Russia's outdoor advertising industry is about 15 percent of all media spend so it is a "big business".
"Things are not always going up – you have to be prepared to be facing crisis and right now, as far as we are concerned, we have invested a lot of money in Moscow contracts and the city hasn't dismantled 40 percent of the (illegal) panels they were supposed to dismantle," he said.
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Decaux said he intends to meet with the mayor of St. Petersburg, to discuss why so many illegal billboards have yet to be taken down.
"Crisis brings opportunities as well, including Russia and I could give you many examples of when we have benefited from crisis – but you need to have the guts and you need to think long term," he said.