Exchange rates were blamed as the group reported first-half revenue of €3.36bn (£2.66bn / $4.53bn), which was a 0.2 per cent increase on the same period in 2013.
As a result pre-tax income dropped 15.3 per cent year on year to €376m (£297m / $507m).
Growth would have been 4.8 per cent at constant exchange rates and was 1.8 per cent on an organic basis.
"These figures are not satisfactory by our standards," said Lévy. "They are not consistent with what our operations can achieve.
"As can be seen from our digital growth [+8.8 per cent] or the numerous awards from various juries [Gunn Report, Gartner and an impressive haul of awards at the Cannes International Festival], our strategy is spot-on and our networks are at the cutting edge of the industry."
He added that growth would be better in the second half of the year but cost control would be the priority in order to achieve a profit margin closer to the group’s goal for the year.
Publicis does not provide detail on its PR revenues, but its new business report for the first half of the year showed that MSLGroup picked up two new clients: Amplificacao and Trident, both in Brazil.
MSLGroup chief communications officer Trudi Harris explained: "The two Brazilian wins are a legacy from before a March 2014 decision by MSLGroup to no longer name new clients publicly, including within the Publicis Groupe quarterly report. We have of course won multiple high value pieces of work in Q2."