The windscreen of Opposition leader Raila Odinga's car was damaged as police dispersed his supporters in Nairobi on Friday.
It was not clear whether the damage was caused by a bullet or a stone.
Crowds took to the streets after Raila jetted back from the US, but they turned chaotic and burned tyres, blocked roads, mocked police and hurled stones at them, threw up burning barricades, sang and danced.
The windscreen was damaged on Jogoo Road as police chased after Raila's supporters.
The NASA principal, who has been termed the people's president, was not hurt and proceeded to Kibra where a rally is expected to take place.
Interior ministry spokesman Mwenda Njoka dismissed claims of attempts on Raila's life.
"Claims of an attempt on Raila's life that are being circulated on social media are false and absolutely baseless," he said via Twitter on Friday.
Njoka said the claims being circulated on verified NASA accounts are to attract sympathy.
They should be "ignored and treated with the contempt they deserve", he said.