Support for Podemos, led by pony-tailed former political science lecturer, Pablo Iglesias, has plateaued after a meteoric rise since being founded in January 2014.
The anti-austerity party has seen support fall from 23.4 percent in March to 17.9 percent in April.
It's once seemingly unstoppable surge has been checked by the centrist party of Albert Rivera who have jumped on the bandwagon of change yet offer a less than radical alternative to the traditional parties with its more liberal economic line.
The survey byMyWord Institute for Cadena Ser showed that Prime Minister Mariano Rajoy's PP were still on top with 22 percent of voting intentions.
The Socialist party (PSOE) came a close second with 21 percent followed by Ciudadanos with 19.4 percent and Podemos trailing with 17.9 percent.
The survey reinforces the dramatic transformation in Spain's political scene which has changed from the traditional two party contest to a four-horse race.
If the survey is reliable it will mean that no party will be in a strong enough position to form a government after the general election - which will be called before the end of 2015.
But the first test will be at the end of next month when voters go to the polls in municipal elections.
Commentators suggest that an alliance could be formed between the PP and the Ciudadanos while others see Podemos and PSOE as potential bedfellows.