The TV ad, created by Euro RSCG London, features a black Citroen C4 being followed by a group of cyclists.
The ad, which highlights the car's "stop-start technology," was challenged by a viewer who thought it could discourage young children from wearing cycling helmets.
Citroen, in its defence, pointed out that wearing a helmet while cycling is not a legal requirement and the cyclists, all adults, were not filmed riding in a dangerous manner.
The advertising regulator said older children might understand the scene in the ad is fantastical and set apart from reality, but younger children would not, and therefore, the ad could encourage them to emulate "a behaviour prejudicial to their health and safety".
Clearcast defended the ad by saying it did not require an "ex-kids" restriction to stop the ad from being shown around children's programming as it did not feature any children on bikes.
The ASA said the ad could be not be broadcast again without the appropriate scheduling restriction, highlighting the authority's increasing sensitivity to advertising's effect on children.