Six were left with minor injuries after a brawl involving 20 to 30 people before the fighting was resolved, said the source, who confirmed no arrests had been made and nobody had yet pressed charges.
Spanish media reported that some construction workers had used wooden poles as weapons in the fight and that those involved had been fired by their employer, an external contractor appointed by Barcelona to tackle the renovation.
The Catalan club previously pledged to return to their Camp Nou home before the end of 2024 but have not yet set a date for it.
"The club is working to have the stadium ready for a return before the end of the year," said vice-president Elena Fort on Monday.
The stadium is set to open with a capacity of 62,000, with the aim of completing the works by the start of the 2026-27 season at an expanded capacity of 105,000.
Since the works began in 2023 Barcelona have played home matches at the Olympic stadium on the city's Montjuic hill.
