A second round runoff between hard-left French presidential candidate Jean-Luc Mélenchon and his far-right opponent Marine Le Pen would be the "worst-case scenario" for France, the chief executive of Publicis, Maurice Levy, one of the world's largest advertising agencies, has said.

"The worst nightmare you can imagine is a second round where you have Marine Le Pen and Jean-Luc Mélenchon. That is the worst-case scenario," he said, speaking to CNBC moments after the release of disappointing first-quarter results for the French multinational agency.