Google executive Wael Ghonim, who emerged as a leading voice in Egypt's uprising, was barred from the stage in Tahrir Square on Friday by security guards, an AFP photographer said.
Ghonim tried to take the stage in Tahrir, the epicentre of anti-regime protests that toppled President Hosni Mubarak, but men who appeared to be guarding influential Muslim cleric Yusuf al-Qaradawi barred him from doing so.
Ghonim, who was angered by the episode, then left the square with his face hidden by an Egyptian flag.
Qaradawi gave a Friday sermon in the square, where hundreds of thousands of people gathered a week after Mubarak's fall, in which he called for Arab leaders to listen to their people.
Ghonim, Google's head of marketing for the Middle East and North Africa, administered a Facebook page that helped spark the uprising that toppled Mubarak's regime.
The 30-year-old also appeared in an emotional television interview shortly after he was released from police custody after 12 days in custody which is credited with re-energising the movement just as it seemed to be losing steam.
In an interview with CBS's "60 Minutes" that aired on Sunday, Ghonim said the protests which led to Mubarak's ouster would not have happened without online social networks.
"If there was no social networks it would have never been sparked," he said.
"Because the whole thing before the revolution was the most critical thing. Without Facebook, without Twitter, without Google, without YouTube, this would have never happened."